Suited-up, catchphrase-spewing Barney Stinson is arguably the best and most popular character Neil Patrick Harris has tackled during his career.

And yet, one mystery has surrounded the character since the very first season. Just who is Barney's father? Apparently, it's John Lithgow.

The accomplished character actor -- who most recently made a splash on television as a serial killer on "Dexter" in 2009 -- has been cast as Barney's long-lost father, and co-star Cobie Smulders can't wait for Lithgow to appear onscreen.

"It's really exciting and different for our show," she said. "He's such a pioneer."

The announcement that the character will finally make his long-awaited appearance isn't much of a surprise to fans.

On a recent episode, Barney finally decided that he wanted to meet his father, following years of clinging to the belief that he was the son of Bob Barker of "The Price is Right" fame. His change of heart was the direct result of the sudden passing of Marshall's (Jason Segel) father.

Television fans may also remember that Lithgow played the patriarch of a group of stranded aliens on the hit comedy "3rd Rock from the Sun," which ran from 1996 to 2001.

In other "HIMYM" news, Nazanin Boniadi -- best known for her three-year stint on "General Hospital" -- will appear in a multi-episode arc as a love interest for Barney.