There are no small parts, certainly not in three-hour Christopher Nolan movies. The celebrated director has a well-earned reputation as an actor's dream, particularly with prestige projects like Oppenheimer, where awards are a non-zero possibility. That explains the presence of a number of A-list actors in small supporting roles. It also gives Nolan and his casting directors plenty of options to choose from.
Source：https://www.cbr.com/oppenheimer-tom-conti-albert-einstein-the-dark-knight-trilogy/
