Willow Rosenberg is a fictional character created for the fantasy television series Buffy the Vampire Slayer (1997–2003). She was developed by Joss Whedon and portrayed throughout the TV series by Alyson Hannigan. Willow plays an integral role within the inner circle of friends—later called the Scooby Gang—who support Buffy Summers, a teenager gifted with superhuman powers to defeat vampires, demons, and other evil in the fictional town of Sunnydale. The series begins as Buffy, Willow, and their friend Xander are in 10th grade and Willow is a shy and nerdy girl with little confidence. She has inherent magical abilities and begins to study witchcraft; as the series progresses, Willow becomes more sure of herself and her magical powers become significant if inconsistent. Her dependence on magic becomes so consuming that it develops into a dark force that takes her on a redemptive journey in a major story arc when she becomes season 6's "big bad", threatening to destroy the world in a fit of grief and rage.

The Buffy series became extremely popular and earned a devoted fanbase; Willow's intelligence, shy nature, and vulnerability often resounded strongly with viewers in early seasons. Of the core characters, Willow changes the most, becoming a complex portrayal of a woman whose powers force her to seek balance between what is best for the people she loves and what she is capable of doing. Her character stood out as a positive portrayal of a Jewish woman and at the height of her popularity, she fell in love with another woman, a witch named Tara Maclay. They became one of the first lesbian couples on U.S. television and one of the most positive relationships of the series. In addition to being the only character other than Buffy herself to appear in every episode, Willow is featured in three episodes of the spinoff Angel, an animated series and video game (both of which use Hannigan's voice), and the comic Buffy the Vampire Slayer Season Eight (2007–2011), which uses Hannigan's likeness and continues Willow's storyline following the television series. Willow was included in AfterEllen.com's Top 50 Lesbian and Bisexual Characters, ranking at No. 7. She was also ranked No. 12 in their Top 50 Favorite Female TV Characters. UGO.com named her one of the best TV nerds. AOL also listed her as the #1 TV witch of all time, and one of the 100 Most Memorable Female TV Characters.

(From Wiki)