Neil Patrick Harris is a noted television actor. He made his claim to fame in the 80's as the title character in Doogie Howser, M.D. His other credits include a parodied version of himself in all three Harold & Kumar movies, the title character in Dr. Horrible's Sing-Along Blog, and as Barney Stinson in How I Met Your Mother. He reprised the latter in "Peter's Progress".
In "No Chris Left Behind" Stinson begins a homosexual relationship with Ted Mosby in How I Met Your Father.
How I Met Your Mother was on King Stewart III's TiVO in "Peter's Progress", and in 1670s/1760s England, television was done in person, so Harris performed the recorded episode with his male castmates. Stewart was not satisfied with the episode, and show as a whole, so the show was deleted by having his guards shoot Radnor, Segel, and Harris.
In a video that Peter finds from his teenage self in "Peter, Chris, & Brian", teenage Peter speculates that as an adult, both he and Doogie Howser must be getting a lot of "ass," a notable miscalculation in that Neil Patrick Harris is openly homosexual.
A live-action image of Harris appears as Peter and the guys hold up a copy of People magazine in "Underage Peter". As they continue to drink, the image changes to continuously hotter women, before becoming Harris in an image from the 2015 Oscars when he took the stage in his underwear.