An old villain returns with a new accomplice in the Len Wein, Adams and Giordano story in Batman 255 (March/April 1974).
Despite the great Adams art, this is not a story I have ever really cared for.
Len Wein brings back Professor Milo, a Batman villain not seen since 1957, and introduces Anthony Lupus, a man who had suffered from great headaches and pain, who Milo has been “treating,” turning him into a werewolf.
Lupus is not an evil man, but has no choice but to follow Milo’s command to kill Batman, or Milo will not provide him a cure.
Lupus turns on Milo, and it look much like he kills the evil doctor, although Milo does return in these pages in 1980. So I guess he was just seriously injured. Lupus gets hit by lightning and vanishes, but we see that he survived. Lupus has returned a few times, but not for decades.