Jack Nicholson in The Departed.

A film that takes place in Boston, all the cast adopt Boston accents, the movie is hectic and full of tension annnnnnd then Jacks character is on screen. no accent, calm, cool, collected like the film just slooooows down for him. he's a supporting actor that makes the film suddenly turn him into the lead. Don't get me wrong it's a great movie but it can feel a little jarring at times.