Which movie was the best from actor/actress

I thought it could be fun to make a thread about the best performance/movie you think a beloved actor/actress has done. I am talking about a memorable performance from a movie and actor/actress that you will remember forever.

If you think of a actor/actress you like, which performance and movie did make you like that person so much?

Which underappreciated performances thats memorable do we have?

I`ll start:
Val Kilmer in Tombstone, the coolest played character since Han Solo. When I see Val Kilmer, I think it`s a damn shame he never got an academy award for his "Doc Holliday". Every scene he is in is cool in that movie. His performance and character that came to life has made me see that movie not just once, but many, many times. After that movie, Val Kilmer was cemented, for me, as a beloved actor ...forever!

https://www.youtube.com/watch?v=trgKeCFmi3M

http://www.ebaumsworld.com/blogs/1993-oscar-best-supporting-actor-for-val-kilmer-for-tombstone/82818546/