Karen was born Jacob Karnofsky in Wilkes-Barre, in northeastern Pennsylvania, the son of Russian-born Jewish immigrants Mae (née Freed) and Joseph H. Karnofsky, a produce dealer [REF].
As a young man, Karen was encouraged to be an actor by U.S. Congressman Daniel J. Flood, who was an amateur thespian himself, recruiting him into a production at the Little Theatre of Wilkes-Barre.