I directed "Cuckoo's Nest" a few years back, and I considered the Chief to be the lead. It's his story. His is the character that grows and changes through the show. McMurphy is just the catalyst.

At least that's what I told the actor I was recruiting for the part.

I told the actor I was recruiting for Nurse Ratched that her's was the lead. Same with the actor I wanted to play Billy. So I guess the lead would be whichever character I'm recruiting for at the time.

But my real answer is that I don't believe in leads in theater. I try to create a team, a 'community' on stage where the contributions of all the actors are equal in importance, if not in line length. The actors who feel they have to be recognized as the lead, I call them divas, then don't usually ever cast them again.