Mike Collins was the guy orbiting the moon while the other two operated the landing module. There’s an interesting interview that was posted at NASA.gov to avoid lots of people sticking microphones in his face for the anniversary. Here’s a quote from him about his role:
This venture has been structured for three men, and I consider my third to be as necessary as either of the other two. I don’t mean to deny a feeling of solitude. It is there, reinforced by the fact that radio contact with the Earth abruptly cuts off at the instant I disappear behind the moon, I am alone now, truly alone, and absolutely isolated from any known life. I am it. If a count were taken, the score would be three billion plus two over on the other side of the moon, and one plus God knows what on this side.
