Fudo wrote:
william morris used the name Gandolf.. but close

Gandalf is, i would think, more likely to come from the old Norse Gandalfr..
quoting Tolkien "and so he was called among Men of the North Gandalf 'the Elf of the Wand' " gandr can mean wand, staff or magic. álfr means elf.
Oops! I forgot he was spelt Gandolf.
It's not my theory though. Tolkien and C. S. Lewis both read Morris' work and borrowed his ideas. Tolkien was heavily influenced by
The House of the Wolfings, a translation by Morris of a Norse saga. I know that the name Gandalf was adapted from Old Norse (specifically using the
Völuspá), but because Tolkien was so heavily influenced by Morris (including
The Well at the World's End), I don't think it's unlikely that Tolkien drew on the name Gandolf. I mean, he clearly based Shadowfax on the horse Silverfax. Anyway, it's just speculation about what went on in Tolkien's brain, so here's a proper QI fact:
William Morris was the first person to write stories set in completely invented (non-dream) fantasy worlds, and he had a huge impact on other major fantasy writers. But, he is more famous today for his wallpapers