In addition to that role, he is best known for the title role in Doogie Howser, M.D. (which is occasionally alluded to on HIMYM). He also portrayed a fictionalized version of himself in the Harold & Kumar films (alongside Kal Penn who played Kevin Venkataraghavan) and starred as the sympathetic villain Dr. Horrible in Joss Whedon's Emmy Award-winning musical web series 'Dr. Horrible's Sing-Along Blog'.