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Alyson Hannigan is an American actress. She is known for her roles as Willow Rosenberg in the fantasy television series Buffy the Vampire Slayer (1997–2003) and its spin-off series Angel (2003–2004), and as Lily Aldrin in the CBS sitcom How I Met Your Mother (2005–2014). Hannigan received a Young Artist Award nomination for her role in the 1993–94 television series Free Spirit.