Gandalf was known as the wisest, although Saruman was the strongest before the War of the Ring.
Gandalf was the wizard who recignised the One ring and asked Frodo to bring it to Rivendell. He himself went to see Saruman who was staying in his tower. But Saruman had betrayed his fellow wizard and held him captive ontop of Orthac until Gandalf was saved by the Lord of the Eagles;Gwaihir.
After escaping he also jounreyed to Rivendell and he was there when Frodo woke up.
As leader of the Fellowship of the Ring he led the companions to the Caradhas and The Mines of Moria until there he was 'defeated' by an old power called the Balrogs who themselves are thought to be Maiar spirits as well. But the old wizard wasn't dead for in the Fangorn Forest the three hunters (Aragorn, Legolas and Gimli) saw him and together they rode on to Rohan and later to Gondor to fight for the freedom of Middle-Earth.
Gandalf's appearance is widely known for many people know him. He is tall with large eyebrows and always wearing a grey cloak and grey hat, very large. He has this wise and powerful aura around him, making him look very mighty.
When he was born and when he died is not known. He has never been married nor did he have children. His best friends were Aragorn, Bilbo and Frodo but every body knew him well. The elves, Galadriel, Elrond, Legolas and probably all the elves in the books, know him as Mithrandir and the book says that Legolas, one of the Fellowship has known him since the elf was young. That means that Gandalf is at least 2931 years old.
With the dwarves he is known as Thark�m.
C�rdan, the ruler of the grey havens, gave Gandalf the ring Narya and this made him a ringbearer and it also gave him permission to come to Valinor.
After the war Gandalf oversaw the reunation of Gondor and sailed with the ringbearers to Valinor. This is the last information that is known of Gandalf the Grey, also known as Gandalf the White.