Alyson Lee Hannigan is an American actress who plays Lily Aldrin in the CBS sitcom How I Met Your Mother. She is also known for her previous roles as Willow Rosenberg on the television series Buffy the Vampire Slayer and flautist Michelle Flaherty in the American Pie film series.

Hannigan was born Alyson Lee Hannigan in Washington, D.C., the daughter of Emilie Posner, a real estate agent, and Al Hannigan, a truck driver. Hannigan is Jewish on her mother's side, and also has Irish ancestry. Her parents divorced a year after her birth and she was raised mostly by her mother in Atlanta.

Although Hannigan had appeared in an industrial film for "Active Parenting" as a baby, as well as starred in a commercial for the Duncan Hines cookie mix in 1978, it wasn't until she moved to Los Angeles, California in 1985 that she formally began her acting career. Living with her mother and attending North Hollywood High School, she successfully auditioned for agents while visiting her father in Santa Barbara.