Who was the backup lunar module pilot of Apollo 11?

Fred Haise was the backup lunar-module pilot for Apollo 11. He was assigned to the backup crew alongside backup commander James Lovell and backup command-module pilot William Anders.

NASA’s backup crews trained to fly the mission if a prime-crew astronaut became unavailable. Haise therefore practiced the procedures required for the lunar module, even though Neil Armstrong, Michael Collins, and Buzz Aldrin ultimately flew Apollo 11. Haise had also served as the backup lunar-module pilot for Apollo 8.

Haise later became the lunar-module pilot of Apollo 13, flying with commander James Lovell and command-module pilot Jack Swigert. An oxygen-tank explosion forced that mission to abandon its planned landing, so Haise never walked on the Moon. He was originally expected to fly on Apollo 14 before crew assignments changed.

James Lovell was a tempting alternative because he was Apollo 11’s backup commander, not its backup lunar-module pilot. William Anders was the backup command-module pilot, while John Swigert was not part of the Apollo 11 backup crew.