A brilliant but volatile and self-absorbed method actor brought in to replace an injured co-star. He frequently disrupts rehearsals, complains about props, clashes violently with Riggan over creative differences, and steals Riggan's personal motivations for the production.
Mike and Riggan are in constant creative and personal conflict, escalating to a physical fight.
Mike is Lesley's romantic partner and joins the cast as a replacement actor.
Sam and Mike develop a secret romantic connection that complicates the production dynamics.