Alyson Hannigan Biography Alyson Lee Hannigan was born on March 24, 1974, is an American actress. She is best known for her roles as Willow Rosenberg on the television series Buffy the Vampire Slayer, Michelle Flaherty in three American Pie films and Lily Aldrin on the CBS sitcom How I Met Your Mother. Hannigan has dated Ginger Fish of Marilyn Manson. She married actor Alexis Denisof (who playe... more.