After watching Luc Moullet's A Girl is a Gun last night, I started mulling over this question: exactly what kind of an actor is Jean-Pierre Léaud? I have someone's comment (was it a critic's, from one of my acting teachers, a film prof's?) to the effect that he isn't an actor stuck in my head. If I squint, I can see what that means - he's not a chameleon, he's not overtly theatrical, and he doesn't play off a star persona à la Belmondo - but obviously he's doing something: Billy le Kid is a different character than Tom in Last Tango in Paris who in turn is a different character than Alexandre in La maman et la putain.
Maybe it's because I'm still under the influence of the Moullet, but I want to say that what Léaud is doing is closer to what Buster Keaton and Jacques Tati do than it is to what Belmondo or Michel Piccoli do.