This should be an easy one. Who was the third man on the Apollo 11 mission? He was the Command Module Pilot who orbited the Moon alone and took this picture of the Eagle ascending with Neil Armstrong and Buzz Aldrin aboard. (Hint: it's his birthday today.)
Happy birthday to Michael Collins, pilot on the Gemini X and Apollo 11 missions.
Related: Al Worden, the Command Module Pilot for Apollo 15, gave an interview to the BBC about what it was like being alone on the far side of the Moon.