This appealing auburn-haired actress specializes in playing shy, geeky characters who somehow manage to be sexy. A former child model, Hannigan segued to acting while in her teens. After a number of TV roles, she came to prominence as a nerdy lesbian witch on Buffy the Vampire Slayer. Both her acting and love life blossomed while on the sci-fi series, as she ended up marrying costar Alexis Denisof. A plum part in the big-screen American Pie trilogy followed, but in 2005 she returned to her small-screen roots to star on the sitcom How I Met Your Mother.