Jessica Chastain Praisesbr Joaquin Phoenix's Acting in 'Joker' Following the release of ‘Joker’ on Oct. 4, br many have come forward to praise Phoenix,br who portrayed Arthur FleckThe Joker in the film. Actress Jessica Chastain, one of the stars of br ‘It Chapter 2,’ was among those singing praise. In a post to Twitter, Chastain called Phoenix’s workbr ‘one of the greatest pieces of acting’ she’s ever seen. The movie reportedly caused her tobr physically react while watching it in thebr theater, a reaction she described as “shook.” Jessica Chastain, via Twitter Chastain also later sharedbr a photoshopped picturebr of herself wearing Phoenix’sbr 'Joker’ makeup on Instagram.