I remember reading something years ago along the lines that the astronauts they would select for a hypothetical mars mission would be a totally different type than the Apollo astronauts.
The Apollo guys were more the cowboy and daredevil type, where for an 18 month space mission you’d need much more level head types.
Not sure if that was a thing NASA had already planned for, but it always made sense to me.
These days astronauts routinely spend months in space, and indeed their selection process and education requirements are rather different—as of course is the whole purpose and character of the manned spaceflight program.
It should be said, though, that Neil was selected as the CDR of the first mission to land exactly because he was not a gung-ho type but instead extremely calm, collected, and not one to make a number of himself. Buzz, on the other hand, was and is a much more hot-blooded personality.
Interesting interview with him from 2011:
This was the premise of MARS-500 mission/experiment.