What was the third astronaut doing on the Apollo 11?

On the Apollo 11 mission, the third astronaut, Michael Collins, served as the Command Module Pilot. While Neil Armstrong and Buzz Aldrin descended to the lunar surface in the Lunar Module, Collins remained in orbit around the Moon in the Command Module, named Columbia. His role was crucial as he maintained communication with both the Lunar Module and mission control, ensuring the success of the mission while also performing critical navigation and systems checks. Collins' contributions were vital for the safe return of the astronauts to Earth.