House of Mystery (1951-) #192
A doctor becomes jealous of the gardener, so he murders him with an ax. When his wife proclaims innocence, he repents and makes the body the recipient of the first plastic artificial brain. He goes to sleep after the surgery only to wake upon the operating table. It turns out the new brain has made the dim-witted gardener into a completely new person with ambitions of conquest. He replaces the wife's brain and plans to do so with the doctor as well in order to begin building a new army of perfect thinkers.