the Necromancer

[lathspell]

No, Gandalf went to Dol Guldur to find out the Necromancer's true identity and found the White Council's worst fear true.

'"Whatever were you doing there?" asked Thorin with a shudder, and all the dwarves shivered.
"Never you mind. I was finding things out, as usual; and a nasty dangerous business it was. Even I, Gandalf, only just escaped. I tried to save your father, but it was too late. He was witless and wandering, and had forgotten almost everything except the map and the key."'

From: the hobbit - An Unexpected Party.

The story is, if I'm correct, also mentioned in UT, but I haven't got the time to search for that now.

greetings,
lathspell