Dr. Varmus Gremp was a Cloud Giant living in a Cloud Castle. This is not a Beatles song, it's real life! He was responsible for the creation and spread of The Gremp, that bastard. He at some point killed the swordmaster of one Braenth of Barovia. The swordsmaster's soul then inhabited one of his blades, which Braenth was made to carry with him, and the two seeked to hunt down and slay the bad doctor.
The Tower of Grey travelled to his home (along with Braenth) in the clouds and fought him, wounding him enough for Rowan Grey to trap him in a Bone Card. Pretty badass, if I do say so myself. And I do. Anyway, the card was then given over to Braenth of Barovia, where his fate remains unknown. Probably not great. Not a great fate. Hehe.