Alyson Hannigan 1989, her first regular role on a TV series came when she was cast in the short-lived ABC sitcom "Free Spirit". As a teenager, Hannigan babysat for the children of her future "How I Met Your Mother" costar, Bob Saget. In 1997, Hannigan was cast to play Willow Rosenberg, Buffy Summers' best friend, on the television series "Buffy the Vampire Slayer". The show became a success, and Hannigan gained recognition, subsequently appearing in several films aimed at teenaged audiences, including "American Pie" (1999), "Boys and Girls" (2000), "American Pie 2" (2001), and "American Wedding" (2003). She also had a guest
Buffy the Vampire Slayer (season 4) Buffy the Vampire Slayer (season 4) The fourth season of the television series Buffy the Vampire Slayer premiered on October 5, 1999, on The WB and concluded its 22-episode season on May 23, 2000. It maintained its previous timeslot, airing Tuesdays at 8:00 pm ET. Beginning with this season, the character of Angel was given his own "series", which aired on The WB following "Buffy". Various "Buffy" characters made appearances in "Angel", including Buffy herself; Cordelia Chase, formerly a regular in "Buffy", and Wesley Wyndam-Pryce, who appeared in "Buffy" season three. Season four sees Buffy and Willow enroll at UC