O'Sullivan, performer in the famed Second City comedy troupe, died Friday afternoon, the Toronto Star reported Saturday.
"This man was just so adored by his family, and everyone who knew him," his partner, and mother of his three daughters, Linda Kash, said. "He was everything to us."
The actor appeared in several Canadian television shows, including "Little Mosque on the Prairie," "An American in Canada," "Getting Along Famously" and "Murdoch Mysteries."
"He was an extraordinarily funny man," said Klaus Schuller, the producer at Second City in Toronto. "But he was also such a generous, caring, giving person to work with. It was a joy to see him walk in the room. The enthusiasm he had for the work was really just exceptional."
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