Adam Rabinowitz (died 2005) was the original Dr. Metronome, a black cape who was active in the 1960s and 1970s. Notably, he was the first costumed villain that Martin Rock-- then the sidekick to the original Green Knight-- ever faced.
Rabinowitz retired from a life of crime and supported himself in his old age as a piano teacher for children and teenagers. When one of his students, Katie Morgan, was nearly drowned by her psychotic mother, Rabinowitz resumed the mantle of Dr. Metronome, using his powers to kill Mrs. Morgan and save Katie's life. In the process, he lost his own.