Michael Shannon Michael Shannon

He plays Boardwalk Empire's federal agent Nelson Van Alden, whose job — crusade might be a better word for it — is to enforce newly enacted Prohibition in Atlantic City. Good luck with that!

Where you've seen him His stunning, Oscar-nominated turn as Leonardo DiCaprio's mentally disturbed yet eerily insightful neighbor in 2008's Revolutionary Road. He's currently delivering a tour de force as a desperate producer in off-Broadway's Mistakes Were Made.

Why we love him It would be treat enough to gaze upon Shannon's granite-jawed, beady-eyed intensity from week to week, but it's the complexity, the myriad conflict, that lie beneath it that make his performance one for the ages. "He is absolutely riveting," says executive producer Terence Winter, who had his eye on Shannon ever since taking in his 2004 off-Broadway performance in the play Bug. "He gets you in the palm of his hand, and you just cannot take your eyes off him."

What's his deal, anyway? "He's definitely got some OCD, that's for sure," says Shannon of his alter ego, whose obsession with keeping booze off the street is matched by his increasingly stalker-ish attentions to Margaret Schroeder (Kelly Macdonald). Explaining Van Alden's (literal) self-flagellation over said crush in Episode 6, Shannon says, "I imagine him being from one of these ultraconservative Christian religions — no dancing, no nothing — and while I think he'd like to be [her] guardian angel, I also think he's very frustrated."

Stay tuned "I had some weird days on this show, that's for sure," Shannon attests. Having gotten an eyeful of where Van Alden's arc is heading in this week's season finale, we can vouch for his assuring us, "It gets weirder, too."  Can't wait for next season!

Boardwalk Empire airs Sunday at 9/8c on HBO

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