Gandalf is a poweful magician, and the worst enemy of the Dark Lord.
Gandalf has been said to be the person most responsible for Sauron's downfall, labouring nonstop for roughly 2000 years to put an end to his reign. Gandalf was the bearer of Narya, the Ring of Fire, given to him by Cirdan when he arrived in Middle Earth.
Gandalf always held Hobbits near to his heart, and he also held their race in high regard. In the year 3001, he set in motion the Quest of Mount Doom. Gandalf was one of the most important people at the Council of Elrond, because he alone knew the full history of Sauron and the Ring. Although he fell battling the Balrog in Moria, he made his way back to Middle Earth as Gandalf the White to complete his errand.
He was responsible for casting Saruman out and taking over as the head of the White Council. After the War of the Ring Gandalf sailed from the Grey Havens with Elrond, Bilbo, Galadriel, Legolas and Frodo.