Do You Know Who's Cool? Diego Klattenhoff

Why He Looks So Familiar Before landing a gig on Showtime’s Homeland as Nicholas Brody’s (Damian Lewis) military buddy, he appeared on NBC’s Mercy and ABC’s Men in Trees.

The Role That Got Away On The Blacklist, Klattenhoff plays special agent Donald Ressler, but when auditioning for the show — after learning his Homeland role would shrink in season 3 — he had his eye on playing enigmatic Tom, the suspicion-raising husband to Ressler’s onscreen colleague, Agent Keen (Megan Boone). “I played a really good guy for two years on Homeland, and I was champing at the bit to play a bad guy.” He didn’t get that role (it went to Ryan Eggold), but playing Ressler offers at least one major perk: shooting a gun! “It is fun,” says Klattenhoff, 34. “I’m not going to lie to you.”

On Mean Girls Being cast in the 2004 comedy, in which he played Regina George’s (Rachel McAdams) projection-room hookup, Shane, was a big deal for the Canadian, who has a German father and an Irish-Welsh mother. (“Diego is just a name they liked,” he explains.) Working with Tina Fey and Lindsay Lohan, he says, was transformative: “You get a taste of how good it can be, and that keeps you going for a while.”