He has many great scenes being the main protagonist, but my favorite is easily the one where he defines the plan to kill Sollozo and McClusky to Sonny, Tom, Tessio, and Clemenza. The way he sits in the chair first shows how he can command and wield power and authority. His way of thought and speech reveals a brilliant strategist. It's the scene that shows his change from the idealistic college boy to a leader of a Mafia family.