One of the others was to serve as best man.

They each served as the best man at the other's wedding.

Did the individual serve as an officer or enlisted man?

John Wayne served as the best man at the wedding.

I served overseas in the Army as an enlisted man.

Ben would serve as Jake's best man at the wedding.

Gallup also served as best man at Smith's wedding in 1988.

Clapton served as best man at their wedding, also in 1973.

Joey served as best man at the ceremony and was delighted with his role.

John Stanford White served as best man for his brother.