Son Goku is the primary hero of the Dragon Ball series. The series started out with Goku as a child of age 12. Once he grew up and his son was born, the TV series' name changed from Dragonball to Dragonball Z. At the end of the series, Goku was roughly 45 years old. Goku is a Saiyajin whose native world is the planet Vegita. He was sent to Earth in a space capsule right after he was born so he could conquer the planet. However, he hit his head and lost his "programming," thus becoming the kinder, gentler Goku we see in the series. Goku was raised as a human on Earth, and did not learn of his true nature until his brother Radits came to Earth... Later, when Goku's rage was awakened by witnessing the death of his friend Kulilin, his Super Saiyajin power was awakened. When he goes Super-Saiyajin his eyes turn green and his hair gold. Currently, Goku can go to the 4th stage of Super-Saiyajin power.
Bulma
Bulma is the second character to appear in the series, and has been a major character in both DB and DBZ. She created the "Dragon Radar" which can sense the location of the Dragon Balls by the radiation they emit, and was the one who first started the se arch for the Dragon Balls. She is also Trunks' and Bra's mother. She is a major influence on almost all of the major characters and is most notably the only character who was able to "tame" Vegita.
Mutenroshi (aka Kamesennin)
Mutenroshi was Goku's first trainer and was once the strongest person on earth. He founded the "Kamehameha" technique which was used A LOT in the series. He's also incredibly perverted; he has a panty fetish and is always trying to find ways to get "peeks " or "feels" of young, beautiful women. However, he has a companion, Umigame, a sea turtle, who tries to curb his "urges." Despite his perverted wishes, Mutenroshi is very old and wise, and has an excellent battle sense. Like many other characters in DB, Mutenroshi played his prime role in the first series.
Oolong
Oolong was one of the earliest characters to appear in the DB series. He is a small pig with the ability to change his shape to whatever he wants for 5 minutes. Then he has to rest for 1 minute before he can shape-change again. Like Mutenroshi, he is als o a pervert with a panty fetish, but he is not nearly as lecherous. Yet another character whose prime importance was in the earlier series.
Pooalu
Pooalu is a floating blue cat that went to the same shape-changing school as Oolong. He (She?) has somewhat of a rivalry with Oolong left over from kindergarten; Oolong had bullied him before getting kicked out for stealing the teacher's panties. Unlike Oolong, Pooalu can do "true" change, and does not need to rest every 5 minutes. Pooalu is also a friend (worshipper?) of Yamucha's. He has always served as somewhat of a minor character in both series, although he has had his high points.
Yamucha
One of the first characters to appear in the series, Yamucha was originally Goku's enemy, but soon became friends with him. Yamucha is characterized by a constantly changing hairstyle and an intense fear of women. (at least at the beginning) He was somew hat of an important character during the first series but less so in the second, being the weakest of all the Z fighters.
Gyumao
Gyumao was Kamesennin's second best student, next to Son Gohan, Goku's "Grandfather." (Goku named his son after his grandfather, so don't get confused) He is a very large man who is always characterized by wearing a horned helmet. He appeared early in th e series, during the first search for the Dragon Balls.
Chichi
Chichi is Gyumao's daughter, who also first appeared about the same time as he did. After the first time we see Gyumao and Chichi they don't reappear for a long time (in the manga). The next time we see Chichi, she gets married to Goku. Therefore, she is also Gohan and Goten's mother. Her distinguishing trait is her temper; she gets mad a LOT. She is a very overprotective mother, which is probably justified in that her son is constantly drawn into fights against some of the toughest people in the unive rse.
Kulilin:
Kulilin is Goku's best friend, and has been around since the first series. He is a fighting monk who leaves his temple to find and train with Mutenroshi. He is kind of short, has no nose and throughout most of the series, has no hair either. Kulilin trai ned with Goku under Mutenroshi and afterwards shared many adventures with him. Kulilin has died more times than anyone else in the series. He is one of the weaker fighters, but this is partially due to his low self-confidence. Nevertheless, he has gotte n fairly powerful due to all his fights with the really powerful enemies, and I think is the next strongest Z fighter after Piccolo.
Lunch
A young, naive girl that Goku and Kulilin saved to bring to Kamesennin. She stayed at the Kame House during the first series, acting as somewhat of a housekeeper. Normally she is a polite, good-natured girl with dark hair, but whenever she sneezes, her h air turns blond and she becomes a psychotic criminal. When "bad" Lunch sneezes, she changes back.
Artificial Human #8
The first Artifical Human in the Dragon Ball series, AH #8 first appeared during the first series, and bears a resemblance to the Frankenstein Monster. Made by Dr Gero of the Red Ribbon Army, he was supposed to kill Goku but would "not do bad things." Go ku saved his life and became his friend, and AH #8 ("Hatchan") helped Goku defeat White of the Red Ribbon Army.
Bora and Upa
Bora is a big man that guards Karin's tower, and Upa is his son. They have Goku's 4-star Dragon Ball, and appear during the Red Ribbon saga. Bora is killed by Taopaipai, sparking a quest where Upa joins Goku to find the Dragon Balls to revive him. After the first series, we don't see Bora and Upa again until the very end of DBZ during the fight with Original Buu.
Karin-sama
A very old, wise cat which lives high on the top of Karin Tower. It is there that he grows the Senzu seeds, magic beans that heal and energize whoever ate them, plus each seed is worth 10 days of food when eaten. Karin-sama also has the Choushinsui, a ma gical but very poisonous tea that grants a large power-up to whoever drinks it and survives.
Uranai-no-Baba (lit. Fortune telling old woman)
Uranai-no-Baba is Mutenroshi's older sister, who runs a fortune telling "business." For 10,000,000 zeni (the DB world's money) you can have your fortune told, or else you have to beat 5 of her fighters to have the future told. She also has the power to a llow someone to come back from the dead for one day. She does this for Son Gohan (Goku's "grandfather") and Goku later on.
Son Gohan
Sorry if this confuses you, there are 2 Son Gohans in the series. This one is Goku's "grandfather" who found Goku abandoned in his Saiyajin space capsule and took him in. Goku squashed Gohan flat when he turned into a giant monkey. Gohan comes back fro m the dead in the series as one of Uranai no Baba's 5 fighters to talk to Goku.
Tenshinhan
Tenshinhan is a 3-eyed man who was a student of Mutenroshi's rival Tsurusennin, from whom he learned a lot of interesting techniques. He can communicate telepathically with his best friend Chaozu, and his master Tsurusennin. Originally he trained to be a n assassin, but eventually realized that being one was not what he wanted. He beat Goku to win the 2nd Tenkaichi-budokai, and was fairly powerful during the first series, second only to Goku. Recently, though, he has taken a subordinate role in the series like Yamucha. Next to Yamucha, he is probably the weakest Z fighter.
Chaozu
A small, pastel-white floating child, and friend of Tenshinhan. Like Tenshinhan, Chaozu is a student of Tsurusennin, and competed in the second Tenkaichi-Budokai in the series. Chaozu is a fairly good fighter, but is not very good at math; this proves t o be his weakness. He is tied with Kulilin for the most number of deaths in the series.
Yajirobe
A friend of Goku's and a minor character in the series who carried Goku up Karin's tower during the time when the old Piccolo was around. For some reason he decided to stay there. He occasionally comes down to supply Senzu seeds. Normally a coward, he occasionally does something brave, like attacking Vegita and cutting off his tail. He is a fairly good fighter in his own right but not up to the standards of Goku and the others.
Mister Popo
Mister Popo is a short, jet-black humanoid with a turban who lives up in the Tenkai and is a servant to whoever is the current Kami of earth. He's been there since even before Kami-sama was there, and is fairly strong, though nowhere near as powerful as any of the other Z fighters.
Kami-Sama
Kami-sama, the god of Earth, created Shen-Lon and the Dragon Balls. He is a Nameck-seijin like Piccolo. Actually, he is Piccolo; he cast away all his evil into the old Piccolo. Therefore, if Piccolo dies, so does he. Kami-sama lives in the Tenka i, a floating palace high above Karin's tower, where he can look down and see what is happening on earth. He no longer exists, having fused with Piccolo to give him a large power-up so he could fight Cell.
Piccolo
Piccolo is Goku's old rival. He was born after Goku killed his father when he was a kid; in his last breath the old Piccolo spat out an egg, and the new Piccolo hatched. Piccolo then went on to fight Goku in the final round of the Tenkaichi-Budokai, which he subsequently lost by a very close margin. Piccolo is a native of the planet Nameck, although he doesn't learn this for quite some time after his first appearance. As a Nameck, he can regenerate almost any part of his body lost. (usually the arms) He can also extend the range of his arms till they're really long. Later, he goes to Nameck to help Kulilin, Goku, Gohan, and Vegita fight Freezer. After the Tenkaichi-Budokai, Piccolo becomes more and more of a "good guy." Eventually he becomes Goku's friend; fairly recently he got pissed off at Trunks and Goten for calling Goku weak. Once one of the most powerful characters in the series, he has sort of reached a "middle ground," neither weak nor strong among the Z fighters.
Son Gohan:
Son Gohan is Goku's first son. At the end of the series he was 26 years old but in this picture he is 9. For a short while after the second time Goku died in the series, Gohan became the primary character. Gohan is the most powerful non-fused character in the DBZ world, but lacks the love of fighting his father has and thus rarely uses his full strength. Gohan is a very good-natured boy and unlike his father, hates fighting, although for a while he was more powerful. He is very polite towards just about everyone except to his enemies, and when he's pissed off. Gohan is very bright and studies very hard, although this is somewhat due to the wishes of his very strict mother. Gohan is the first character in the series to have gone Super Saiyajin-2, during the Cell Game; the power of his anger was kindled by watching his friends get beaten up, and the death of Artificial Human #16 sent him over the edge. It was roughly at this time that the series switched main characters from Goku to Gohan.
Vegita
Vegita is the "bad guy among the good guys." He first made his appearance back when Gohan was 4. Although he fights alongside the other Z fighters, he is still decidedly evil. As the prince of the Saiyajins, he is very proud, has a huge ego, and is constantly trying to prove that he is the best fighter in the universe. Vegita has a continual rivalry with Goku, or "Kakarott," (Goku's Saiyajin name) and is obsessed with beating him in combat just to show that he is the stronger. This obsession with trying to be stronger than Goku proves to be a fairly large weakness as well. Despites his efforts to show otherwise, Vegita has changed and has developed a conscience, and deep down cares about his friends. Furthermore, he is also somewhat emotional at heart. He demonstrates this when dealing with his son Trunks, most notably just before he died trying to kill Majin-Buu. Although he pretends to hate Goku with a passion in reality he respects his power and maybe even likes him a bit.
Enma-sama
Enma-sama is a huge man that guards the entrance to the afterworld. He sits at a desk and sends all the spirits that come there to either Tenkoku (heaven) or Jigoku. (Hell) He plays a fairly minor role in the series but often deals with what happens to dead main characters, allowing them to return to Earth, etc. Note that Enma is actually a figure from Shinto religion, the King of the Afterworld.
Kaio-sama
One of four Kaios, beings from each corner of the galaxy who monitor activity in their sector of the galaxy. He lives on a ridiculously small planet (ever read "The Little Prince?") at the end of a long road in Heaven. He has a pet monkey Bubbles and in the TV series, a pet insect of some sort, Gregory. The first time Goku died, he trained with Kaio-sama and learned the Kaio-ken and Genki-dama. Kaio's planet was destroyed when Cell blew up on it.
Dende
Dende is Kami-sama's successor as the god of Earth. Like Piccolo and Kami-sama, he is also a Nameck-seijin, and is even younger than Gohan. Gohan and Kulilin first met Dende on their trip to Nameck-sei to gather the Nameck Dragon Balls. He has the power to heal injuries by laying his hands on the injured, and created more powerful Dragon Balls on Earth that can grant three wishes.
Nail
A minor character during the Nameck-sei episodes, Nail is the bodyguard of Saichoryo, the planet's elder and source of life for the Dragon Balls. He fused with Piccolo to give him a power-up to fight Freezer.
Trunks
Trunks is Vegita's son. In his future, all of the Z fighters were killed by the Artificial Humans, except for Goku, who died of heart disease. Trunks travels 20 years back in time to give medicine to Goku so he can survive this disease and defeat the Artificial Humans. Trunks' returning in time alters the past in other ways which can be seen later. After giving the medicine to Goku, Trunks goes back to his own time, but returns again three years later to help the Z fighters battle the Artificial humans. During this time, he becomes extremely powerful and surpasses every other one of the Z fighters except for Gohan and (maybe) Goku. The Trunks here, "Future Trunks" and the "current Trunks" are radically different characters. "Future Trunks" is very polite like Gohan and has very strong values, but the current "Chibi Trunks" has a bad attitude and is somewhat like his father. Chibi Trunks never truly reaches the power level of his future counterpart; possibly because he lived through mostly peaceful times, whereas Future Trunks did not.
Artificial Humans #17 and #18
These two Artifical Humans were also created by Dr. Gero to kill Goku. They are twin brother and sister, #17 being a man with long black hair, and #18 being a girl with blond hair. In Trunks' future, they are both very much "bad guys," having wiped out m ost of the population of Earth. However during the altered timeline they are less destructive, focusing just on killing Goku. They end up joining the Z fighters to fight Cell, as Cell wanted to absorb both of them. Cell absorbed both, which was the last time we ever see or hear of #17 until the very end of the manga series, but Cell eventually spits out #18. Later on after Cell is killed, #18 marries Kulilin.
Artificial Human #16
AH #16 is a very large robotic man with a red mohawk and green armor. He was made by Dr. Gero to kill Goku as revenge for destroying the Red Ribbon Army, but joined the Z fighters to fight Cell. He is normally very quiet and introverted, and possesses a strong love and respect for nature and life. His death at the hands (feet?) of Cell was what triggered Gohan to go Super Saiyajin 2 for the first time.
Mr. Satan
Used mostly as comic relief, Mr. Satan is the "hero of earth," taking credit for having killed Cell and saving the planet. Among "normal" Earthlings, he is fairly strong, but in reality he is a weakling and a coward. However, he performs the occasional heroic action, and occasionally manages to save the rest of the Z fighters by some minor action. He is also one of the only characters in the Dragon Ball series who has never died.
Beedel
Beedel is Mr. Satan's daughter, and is the same age as Gohan. While not nearly as strong as any of the other Z fighters, she is a lot better than her father. She is in Gohan's high school class and uncovers his identity of "Great Saiyaman." Eventually sh e and Gohan get married.
Son Goten:
Goten is Goku's second son, and a dead ringer for Goku when he was a little kid. At the end of the series, Goten was 17 and looked nothing like Goku though. Goten is very powerful for someone his age, although he is a little bit naive like his father. He can fuse with Trunks to become Gotenks, one of the most powerful characters in the series.
Maron
Maron is Kulilin and #18's daughter with a very round head and pigtails. She plays a very minor role in the series. (in fact, we don't even learn her name until long after she is first introduced) There's not too much more I can think of to say about her.
(East) Kaio-shin
Kaio-shin is one of four gods of the Kaios. Most of the other Kaio-shins were killed off by Majin-Buu, and one was imprisoned within the Zed Sword. (We actually get to see this one) Kaio-shin then traveled to Earth to stop Babidi from reviving Buu, and enlists the help of the Z fighters. However, his plan to stop the revival backfires...
Kibito
Kibito is Kaioshin's assistant. He has the power to heal wounds with his hands much like Dende. He plays a fairly minor role in the DBZ series. Eventually using 15-dai-mae Kaio-shin's earrings, he fuses with Kaio-shin permanently.
Majin-Buu
Majin-Buu was one of the strongest villians in the Dragon Ball/Dragon Ball Z universe, but he eventually became a good guy. He has gone through more different forms than Freezer and Cell combined. The first Buu is fat Buu, a fat, round pink man with a c ape and the mind of a baby, but is very strong. When he got really angry, the smoke that came out of his head changed into Skinny Buu. Fat Buu (who became a good guy around this point) tried to change him into a chocolate, but Skinny Buu blew the blast back at him. Fat Buu turned into a chocolate, Skinny Buu ate him, and turned into Super Buu.
15 Dai-mae Kaio-shin (lit. Kaio-shin from 15 generations ago)
15 Dai-mae Kaio-shin was the Kaio-shin trapped in the Z Sword. When it broke, he was released. Like Mutenroshi, he is a real pervert, but he has an interesting skill; he can give a huge power-up to anyone who can sit through a 25-hour power-up. He uses this skill to make Gohan the most powerful non-fused character in the series.
Gotenks
Using the Fusion, Goten and Trunks can fuse into Gotenks. Gotenks is very powerful, second only to Gohan and Vegitt, and also is the only character other than Goku that can change to Super Saiyajin 3. However, he has a huge ego which gets him in trouble . Gotenks is often used as comic relief as well.
Vegitt
When Goku and Vegita fuse, they become Vegitt (Vegita+Kakarott=Vegitt), the most powerful character in the DBZ world. (I've also seen his name as Gogita, but this is from a DBZ movie and not the original manga.) Like Gotenks, Vegitt has a huge ego.
Pan
Pan is Gohan and Beedel's daughter. She first appears in the last two installments of the manga before it ended. Needless to say, we never get to learn a lot about her before the series ends. She looks just like Beedel did at 16, just a lot smaller. Sh e's pretty tough in a fight for her age and size, and certainly has the potential to become fairly strong.
Bra
Bra is Trunks' little sister. She looks like a carbon copy of Bulma when we first see her way back in DB book #1, only much smaller. Like Pan, she only appears in the last two installments of the manga and only speaks a single line in those installments so it's tough to say much about her.
Uub
Uub is a polite little kid with a mohawk, another character who doesn't appear until the very end of the series. Actually, he is the reincarnation of Original Buu. (Uub=Buu backwards) He is very powerful for a human his age. At the end of the series, U ub goes back to his home town with Goku, who is going to train him.