'How I Met Your Mother' guest John Lithgow: 'If this weren't a comedy, it would be 'East of Eden''

john-lithgow-how-i-met-your-mother-320.jpgIgnoring for a moment the not-so-small matter of an unknown bride, the identity of Barney's ( Neil Patrick Harris) dad on "How I Met Your Mother" is possibly the biggest unanswered question of the series -- and definitely of Season 6. But on Mar. 21, we'll finally come face-to-face.

Emmy and Tony winner John Lithgow makes his first appearance in "Legendaddy" as the Barney's estranged father, Jerry. And speaking with Zap2it about his two scheduled appearances, Lithgow explains that the serious themes explored this season keep coming with his cameo.

"It is very intense," Lithgow tells us. "If this weren't a comedy, it would be 'East of Eden' or something. He's the lost father. There's a pool of serious emotional stuff underpinning all of the comedy. [Barney] is what he is, in so many ways, because he was abandoned by his father. We make comedy out of that, but it's not necessarily the stuff of comedy. What's great is that there are moments in it that are extremely touching. They've set this show up in such a way that it allows for that."

An admitted fan, Lithgow realizes that this has been a running thread in the transitional sixth season, which has seen both Barney's journey to find his dad and Marshall's loss of his own to a sudden heart attack. But as much as that appeals to him, he's here for laughs.

"It just seemed like a wonderful thing to do as a counterpoint to 'Dexter,'" he says, referring to his most recent TV role. "'Dexter' still resonates and hangs in the air. I thought it would be a great idea to do a lark-y thing like this."

Hard as it is to imagine, Lithgow's run as "Trinity Killer" Arthur Mitchell on "Dexter" concluded more than a year ago. But that has not erased many fans' perception of the actor or the reaction from the acting community.

"Boy, it was overwhelming," Lithgow says of his Emmy-winning role. "And I would say that's even the cast while shooting it. I had no idea the impact it would have. You didn't even see much of the character for the first 6 of the 12 episodes. It sort of kicked in halfway through, although the few things that you saw early on were so horrific that you every time you even saw this man's face you felt a sense of terror."

Terror isn't something most people had probably never associated with Lithgow before. He writes books of poems for children, starred as a displaced alien in the sitcom "3rd Rock From the Sun" for six seasons and, perhaps most notably, is one of the most celebrated theater actors working today.

The theater connection between Lithgow and Harris begs the question of whether we can expect some sort of musical performance during his "HIMYM" run. We asked, but he largely dismisses the notion, only offering a little tease: "I do a little dancing, but to comic effect. I'll leave it at that."

With another two seasons locked down for the show, it's also fair to assume we could see more of Lithgow's character in the future.

"Ive just started shooting my second episode, and that's, as far as I know, all I'll be doing," he says. "But I didn't even know I'd be doing the second one... I got the offer halfway through shooting the first. They may think of me again, and I enjoy doing the show so much, I would certainly do it."

Showrunners Carter Bays and Craig Thomas, please take note. 

Photo/Video credit: CBS