Thomas Patrick Lennon (born August 9, 1970) is an American actor, comedian, writer, director and producer. He played Klaus, the man who was set to marry Victoria before she left him at the altar to run away with Ted in the season 7 finale. 
In 1991 he began his career as an actor with the film Aisle Six. He is very well known for his role in the movie 17 Again with Zac Efron, but he is mostly seen in supporting roles in dozens of TV shows, including Reno 911, The League, Children's Hospital, Archer, New Girl, Comedy Bang Bang, Don't Trust the B---- in Apartment 23, and Friends.
He has also appeared in supporting roles in dozens of films, including Bad Teacher, Memento, How To Lose A Guy In 10 Days and I Love You, Man. He played a doctor in two of Christopher Nolan's films: Memento and The Dark Knight Rises.