Guth'Alak is the druid in Terinyo.
He is the one who asks you to find and kill his evil counterpart, Keethrax, who is found in another dungeon to the southeast of Terinyo. Keethrax can be hard to kill for a character without a torch, as he can cast darkness. Keethrax's loot will include the Black torc, an autocursing artifact, still good as "ratling fodder". This quest excludes the Save Yriggs mission.
Later in the game, at experience level 30, Guth'Alak offers another quest (which does not require the player to have done his earlier quest). In it, the player is asked to find and help the Greater White Unicorn, Yrruir.