The other day, I was watching the Coen Bros. version of The Ladykillers (shut up, it'd been a while and I had forgotten), and I kept getting distracted by an itchy question. Is there a character actor, either working today or in the past, that is 1) capable of more range and 2) capable of moving from supporting roles to leading roles and back so seamlessly as J.K Simmons? The first time I saw Simmons in anything, it was as one of the shrinks on Law & Order, and since then, the man has been second to none in every role he's taken. It's pretty much a guarantee that if he's in the cast of a film, he'll be the best thing in it despite the quality of the rest of the film (see the aforementioned Ladykillers, Jennifer's Body, Juno, pretty much the rest of his filmography).
Up until now, his best work has been as J. Jonah Jameson in Sam Raimi's Spider-man films (a role he continued in two separate Marvel animated series, and single handedly kept the character from reappearing in the Amazing series of films). That will probably change with the release of Whiplash (written and directed by Damien Chazelle), where Simmons plays an abusive Jazz instructor, who torments Miles Teller into emotional insecurity. And it looks fantastic. Not big on laughs, but potentially a great character-focused film.