Who was the third astronaut on Apollo 13?

The 3 astronauts who flew on Apollo 13 were Jim Lovell (Commander), Fred Haise (Lunar Module Pilot), and Jack Swigert (Command Module Pilot). Swigert replaced Thomas "Ken" Mattingly 3 days before the launch of Apollo 13 when it was discovered that the son of Charlie Duke, the backup, had caught the measles. Mattingly had not had the measles before, so he was replaced on the flight by Swigert. Apollo 13 was Swigert's only flight. He resigned from NASA in 1977. In 1982, he ran a successful campaign for House Representative from the state of Colorado. Unfortunately, he died of bone cancer 8 days before he was to be sworn in. Lovell and Haise are still alive.