If fans don't go gaga for this latest iteration of Harley Quinn, it clearly won't be the script's fault. Despite Joker: Folie Deuxs endless and sometimes tiring rewrites, Lady Gaga relished the creative process of fashioning the perfect screenplay as both a cool and liberating one. In Arthur Fleck's (Joaquin Phoenix) latest big-screen adventure, Gaga is tasked with the awesome responsibility of portraying one of the most beloved DC characters in director Todd Phillips long-awaited sequel.