Prosky, a Polish American, was born Robert Joseph Porzuczek in the Manayunk neighborhood of Philadelphia, Pennsylvania, to Joseph and Helen Porzuczek. His father was a grocer and butcher. He was raised in a working-class neighborhood and studied at the American Theatre Wing, later graduating from Temple University. He performed at Old Academy Players, a small theater in the East Falls section of Philadelphia, adjacent to Manayunk.
Prosky, a Polish American, was born Robert Joseph Porzuczek in the Manayunk neighborhood of Philadelphia, Pennsylvania, to Joseph and Helen Porzuczek. His father was a grocer and butcher. He was raised in a working-class neighborhood and studied at the American Theatre Wing, later graduating from Temple University. He performed at Old Academy Players, a small theater in the East Falls section of Philadelphia, adjacent to Manayunk.