Which of the three astronauts of the Apollo 11 spaceflight did NOT walk on the moon?

The story behind the answer

Michael Collins did not walk on the Moon. During Apollo 11, he piloted the Command Module, Columbia, in lunar orbit while Neil Armstrong and Buzz Aldrin descended in the Lunar Module, Eagle, to make the first human moonwalk on July 20, 1969. Collins handled navigation, systems, and the critical rendezvous to bring his crewmates home.

Context tip: Collins spent hours alone when Columbia passed