Clueless (1995)
Amy Heckerling's 1995 Beverly Hills Emma adaptation. Alicia Silverstone, Paul Rudd debut.
Paul Rudd broke through in Clueless and has worked more or less continuously since, mostly in comedy, and became a running joke for appearing not to age.
The Apatow films, Anchorman, The 40-Year-Old Virgin and Knocked Up, established a specific register: a decent man whose decency has a thin layer of exasperation over it.
Ant-Man gave him a franchise and a screenwriting credit on both of the first two films, which is unusual for a studio lead.
Wet Hot American Summer and Role Models are where the comic instinct is clearest, and he is very good in the serious parts he rarely takes.