grammar - Whom or Who in this sentence: These men, all of WHOM or WHO were well-known, well-respected statesmen, were viewed by their peers

Here's the full sentence: "These men, all of who were well-known, well-respected statesmen, were viewed by their peers and common people alike as great thinkers in their day.

I just can't really see where it would fall into: subject? predicate? object? What would it be?