Sean Bean

Sean Bean takes the term workaholic to a new level on TNT's Legends.

The latest action series from Howard Gordon (Homeland24) follows Martin Odum (Bean), an agent in the FBI's Deep Cover Operations division who becomes so enmeshed in the personas ("legends") he adopts that the lines between his real and fictional identities start to become blurred.

"This guy ... has a kind of personality disorder, to put it mildly," Bean tells TVGuide.com. "He's a very driven man who creates characters and people from his past experiences. He's very good at it and he totally immerses himself, to a point where he kind of pays quite a big price psychologically."

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Based on the book Legends: A Novel of Dissumulation by Robert Littell, Legends starts off with Martin six months into an undercover assignment to thwart a terrorist attack. (Gordon knows his strengths, and doesn't stray from them here.) For this case, Martin's been posing as Lincoln Dittmann, a geeky pseudo-anarchist who speaks with a stutter but whose rage simmers just underneath his nebbish-y surface. After his cover is nearly blown during a botched sting operation, Martin finds himself being followed by a vagrant who ominously warns him, "There is no Martin Odum." Wait a second, that's his true identity ... isn't it?  As Martin begins to investigate the man's disturbing claims, the trail leads him to various (literal) dead ends.

At the same time, it becomes apparent that Martin's on-the-job method acting may be turning into full-blown split personality disorder. It turns out that several psychiatrists deemed Odum unfit to continue with his undercover duties, and his estranged wife Sonya (Amber Valletta) even points out that he's signed a check with Lincoln's name. The role is an acting tour de force for Bean, who hints at possible cracks in Martin's psychological foundation in early episodes by flitting in and out of characters — all of whom, by the way, have intricately-crafted backstories with official records planted by the FBI to back them up — as if he's turning a light switch on and off.

"Playing someone who doesn't know who they are playing various other characters, for me as an actor, it's a wonderful opportunity to try and get inside someone's head and try and invent something very interesting," the Game of Thrones alum says. "[When] meeting people ... I try and absorb things like a sponge, because they might be used at a later date. That's what I do as an actor to try and build up a character. And that's very similar to what Martin Odum does. So there's kind of that parallel, which I find fascinating."

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Adds Bean's co-star Ali Larter, who plays Martin's strait-laced, by-the-book FBI boss (and one-time bedmate) Crystal McGuire: "He brings such a gravitas to the show and such a weight to it, but there's also this vulnerability in his eyes that makes him so, so interesting to watch."

As the series progresses and viewers get to know Martin's legends — there's the aforementioned Lincoln, a charismatic playboy named Dante and, later in the season, the flamboyant journalist Sebastian Egan — we learn incredibly little about Martin himself, aside from his devotion to his son Aiden (Mason Cook) and a past, brief romantic connection with Larter's character. "He lives a very solitary existence," Bean says. "He's a bit of a lone wolf. ... He doesn't want to be Martin sometimes, and he finds it a relief to go into character and to get under the legends' skins. He feels happier there. He feels more alive and more himself in his legends than he does in real life. Maybe that's because he's got more control over his legends. He can point them in the direction he wants to go in, where his [real] life is in turmoil."

In meeting with real-life undercover agents, Bean said he was taken aback by tales of "the psychological toll [the career] takes upon an individual." (Although, as he points out with a laugh, "I'm just playing an actor playing these guys. I'm not going to get a bullet in the back of my head. So I'm sure they've got to be a lot more convincing than I am.") Legends raises the question: at what point, if ever, does an individual agent's mental well-being outweigh the need to maintain national security?

"Martin's always going rogue, so [Crystal] has to clean up his mess and keep secrets, and that's just not the way that she likes to operate," Larter says of her character. "Crystal likes to follow the rules. She likes to follow protocol. At the same time, she's constantly in conflict because she respects him and is in awe of him as an agent, because his talents are so incredible. So it's that constant tension that we play on."

With Bean having famously been the victim of several on-screen deaths, the actor says he welcomed the opportunity to bring so many characters to life. "I was very happy to be invited to participate in creating these characters," he tells TVGuide.com. "I just tried to, more than anything else, get inside their heads first and work from the inside out. The costume and the physical attributes always came later. But I think I managed to kind of create subtle distinctions without making them comical. It's more of a psychological switch than anything else."

"It's just such a joy to be able to go into work every day and say, 'Who's going to turn up today?'" Bean adds. "It's a real dream of a part."

Legends premieres Wednesday at 9/8c on TNT. See why the show is our Watch This Tonight editors' pick below: