When "Mission Impossible" debuted in 1966, he landed a starring role, as undercover team leader Daniel Briggs. But he left after one season when the show's shooting schedule interfered with his observation of the Jewish Sabbath. He was replaced by Peter Graves.
Without any explanation within the storyline of the series, Hill’s Dan Briggs was replaced by Peter Graves’ Jim Phelps at the beginning of the second season.
Peter Graves was an actor who's generally known for two performances; Jim Phelps on the hit TV show Mission Impossible, and Captain Oveur from the spoof Airplane.