Biographies of each of the current Thieves can be found on this page. At the bottom, you will find a link to a page that will introduce you to members of the Guild who have died.
THEOREN MARCEAUX: Theoren, or Theo as he's known in the Guild, is currently the co-third-in-command of the Unified Guilds. He made his first official appearance in Gambit #17, although I think he was also one of the thieves who helped Gambit and Blade defeat the vampires in Gambit #4. Theo holds the Thieves Guild title "Harvest Master", which means he is responsible for deciding which of the items the Guild steals are kept and which are sold. Theo and his younger brother Etienne, who was killed at age thirteen in 1991, are two nephews of Jean-Luc LeBeau, former Guild patriarch. Theoren's grandfather, Rouler, and father, Belize, both served as Harvest Master in the Guild before Theo, under Jacques LeBeau and Jean-Luc LeBeau respectfully. Theoren takes his job very seriously and acts as a protector to the thieves when Remy's not around. He has been known to step in when Gris-Gris and Emil have gotten into disputes. Theoren is also a computer expert. His specialty as a thief is stealing information off computer harddrives.
MERCY LEBEAU: Mercy is the widow of Remy's older brother Henri LeBeau and daughter-in-law of Jean-Luc. She was the first woman in the history of the Thieves Guild to be allowed to partake in the tilling and, when she successfully completed the job, was the first woman to join the Guild as a thief. Her first appearance in the comics was in Gambit #17. Nothing is known about Mercy's family except for her in-laws, althought it is assumed that she is from one of the now-defunct Guild clans. She often takes a leadership role within the Guild, especially with her fellow Thieves. Nothing is known about her specialty as a thief, although she does use her looks as a distraction to allow the men to slip in where they need to go undetected during jobs.
CLAUDE POTIER: Claude is the last surviving member of Clan Potier. As far as I know, he is the strongest thief, physically, and uses that to his advantage during jobs. Very little was ever revealed about Claude in the comics. He was also very quiet, which leads me to believe he's more introverted and observant than the rest of the thieves. He looks similar to Jean-Luc, which makes me believe that his relatives in Clan Potier are somehow related to Clan LeBeau.
GENARD ALOUETTE: Genard holds the title of Harvest Disseminator within the Thieves Guild, making him the thief with the third-highest rank, below Remy (as Patriarch), and Theoren. His job as Harvest Disseminator is to take stolen items the guild does not need or want to keep and sell them or give them away. In essence, this makes him the business man of the Thieves Guild. Besides this, very little was revealed about him in the comics. It can be assumed that his father held the title of Harvest Disseminator before him. I get the impression that he doesn't actually go on jobs as a thief very often; he even spent one group-related job back at the safehouse with Tante Mattie, for reasons that were never revealed, even though it appeared that he was standing guard over the traiteur.
ZOE ISHIHARA: Zoe was originally a member of the Tokyo Thieves Guild. She was excommunicated from that Guild by her uncle, the Guild Patriarch, when she tried to stop her family from exploiting her little brother Shirow, who is a mutant. They came to America and Zoe sought refuge with the New Orleans Guild by invoking the International Guild Charter. Because she did this, Jean-Luc had no choice but to help her and Shirow and give them a safe place. He also called in his son Remy when Zoe and Shirow were kidnapped by the Pig. This kidnapping resulted in the deaths and injuries of several thieves. Zoe's first appearance was at the end of Gambit #5. She is a much more skilled fighter than the rest of the thieves, something which has earned their respect during her time with them. It can be assumed that Jean-Luc made her an official member of the New Orleans Guild, in spite of her excommunication from the Tokyo Guild.
EMIL LAPIN: Emil can more or less be described as the Bobby Drake of the Thieves Guild. He is a nephew of Jean-Luc, which makes him a cousin of Remy and Theoren. He, Remy and Theo's younger brother Etienne, grew up together and got into a lot of trouble over the years. Emil is considered by the Guild...especially the Assassins and his older cousin Theo...to be a smart-mouthed, obnoxious fool. This often gets on the nerves of Theo and Gris-Gris, but Emil can always count on Remy and Mercy to bail him out. He is a computer expert, just like Theoren is, only his specialty is hacking into computers and getting past security systems and the like. The way he acts, it can be assumed that he is the youngest member of the Thieves' family, with the possible exception of Zoe. At the least, he's the youngest of the New Orleans-born thieves. He made his first appearance in the Rogue Limited Series and even back then it was shown that above all else he is loyal to Remy and will even break Guild rules to help him.