Gandalf the Grey was first known as a "disturber
of the peace" when he came to present Bilbo Baggins
a burglar job, and a grand adventure.  Although
Bilbo attempts to politely decline, he is somehow
pushed into it.  Gandalf helps the dwarves and 
Bilbo to their destination, which is Lonely Mountain.
However, that is only a small story in Gandalf's long
tale.  For now, I will summarize his role in Lord
of the Rings.  He came to Bilbo's party, and spoke 
with him about the handing down of the ring.  Then
he left to do some research of his own on this 
mysterious ring.  He finds it is the one ring that
the Dark Lord, Sauron has been seeking for all these
years.  He goes to the shire and tells Frodo, and they
decide that it must be taken to Rivendell.  He tells 
Frodo he will meet him at Bree, and goes to see the
head of his order, Saruman.  When he arrives, however,
he learns of Saruman's betrayal, and Saruman traps
Gandalf there, so he cannot stop Saruman.  He manages
to get free, and heads to Rivendell to meet Frodo.
They then hold the council of Elrond where it is 
decided that the ring must be destroyed.  Gandalf
is one of the nine walkers, against the nine that 
were sent from Mordor.  However, along their journey,
they must go through Mordor, and Gandalf falls with
the Balrog.  Thinking Gandalf is lost, the rest of
the company reluctantly go on ahead.  Later, Gandalf
makes his return in Fangorn Forest, where he meets
Aragorn, Legolas, and Gimli, who are tracking Merry
and Pippin at the time.  He lets them know they are
safe, and they ride to Rohan to see King Theoden.
After Gandalf releases Theoden from the spell that
Saruman has cast upon him, Theoden must move his people
to Helm's Deep.  Gandalf goes to find Eomer and his army.
He rides on Shadowfax, a horse that is wild, but will
bear only Gandalf. He returns in the knick of time with
the army, and the battle is won.  They then go to 
Isengard, where they meet Merry and Pippin.  Gandalf
takes Pippin, and they ride to Minis Tirith, where
they participate in the fierce battle that is won.
When Aragorn arrives with re-enforcements, they
then plan their march to Mordor, hoping that it will
play as a distraction for the two hobbits on their
way to Mount Doom.  It proves successful.  Just as 
Sauron releases his army, the ground crumbles, and
they find the ring is destroyed.  Then the eagles 
come and bear Gandalf and the other men away.  After
the crowning of Aragorn, later, Gandalf sails on the
white ship with Bilbo and the other elves, never to
be seen again.