Michael Collins piloted Apollo 11's command module Columbia while Armstrong and Aldrin explored the Moon.
Collins remained in lunar orbit while the lunar module Eagle descended to the surface on 20 July 1969. His job included maintaining Columbia's orbit, operating its systems and preparing for the rendezvous with Eagle.
Unlike the astronauts who walked on the Moon, Collins never landed. He completed 30 lunar orbits alone before Eagle returned and docked with Columbia. The mission's three crew members were Neil Armstrong, Buzz Aldrin and Collins.
A common mix-up is confusing Collins with Jim Lovell, who piloted the command module on Apollo 8, or with Apollo 11 commander Armstrong. Collins later became director of the National Air and Space Museum.