A prestigious surgeon suffering from terminal cancer, he was approached by his colleague Derek McDowell with the body of Frankenstein's Monster, which he could animate at will. McDowell tried to use the Monster to get a healthy body and then transplant Wallach's brain to it - to do so, the Monster killed people per McDowell's commands. Although Wallach had developed a machine to automate the transplant, he did not share this secret with McDowell.
Unable to get useful bodies that way, McDowell then transplated Wallach's brain to the Monster itself. The psycho known as Master of Freaks was secretly monitoring Wallach's lab and he disliked the idea because he needed the Monster's brain in the Monster's body for his own ends. Anyway Wallach was enraged at being in a hideous body, and he murdered McDowell for this. He also murdered his nurse, a witness. Wallach threw McDowell's body to the river.
He then went to a circus, where his aspect would go unnoticed, and found a male trapezee artist, James, whose body he intended to use. His appearance startled James' companion Gretchen, who fell to her death. Wallach then knocked out James and took him to his lab, to perform the operation. Once there, he broke a mice jail for the sadistic pleasure of seeing the animals suffered.
Wallach then started the automatic transplant to James, but one little mouse had survived his rampage and climbed through James' inert body, unaware of the sabotage it was performing. Once the transplant was done, Wallach's brain was physically in the body of the mouse, and the Monster of Frankenstein was being controlled by an animal. The Monster then smashed the body inhabitted by Wallach.
Days later, Sinoda used voodoo magic to bring McDowell's body back to life. The zombie first tried to get revenge on Wallach, by taking the brain from the Monster - only to discover that Wallach was already dead.