Joseph Merrick suffered from a disfiguring disease and became famous as a sideshow curiosity in Victorian England, where he was nicknamed The Elephant Man.
The Hangover star admits he felt a strange kinship with Merrick, and would often look in the mirror as a kid and imagine his face to be deformed too.
Recalling David Lynch's 1980 movie The Elephant Man, Cooper tells Details magazine, "I became obsessed with this motherf**ker. I was crying. I couldn't move. He was a beautiful guy, f**kin' beautiful. He had tremendous hope. He struggled to be a man - because he was a man."
Cooper says the connection has continued throughout his career - he played Merrick on stage for his graduate thesis at the Actors' Studio Drama School in New York, and he's gone through great lengths to get closer to the legend.
He adds, "I literally went to London and saw the cloak that Merrick wore."
Merrick was 27 when he died in 1890, due to accidental asphyxia, caused by the weight of his head as he lay down.