First introduced in "Buffy vs. Dracula," Dawn began as the little sister Buffy supposedly always had, but we never knew about. As revealed in "No Place Like Home," Dawn is a collection of energy brought together in a human form and known as the "Key." Monks sent her to Buffy in the form of a sister to ensure the best possible chance that the Key would be protected by those who want her power. While Buffy, Giles and Joyce have all since found out the truth about Dawn, the young girl has been kept in the dark through it all.

Living on a Hellmouth with your sister being a vampire slayer hardly equals a normal life. Ever since Buffy found out that Dawn was not really her sister, she has been extra careful to protect Dawn from any potential danger. Dawn continued to grow more suspicious as people continued to question who she is and tell her she doesn't belong. Fianlly in "Blood Ties" Dawn finds out she is the Key and freaks out by cutting her wrist and asking Buffy what she is. Buffy tells her that she is her sister, they have the same blood : Summer's blood. In the Gift it was revealed that Dawn's blood was the Key and knowing this she wanted to sacrifice herself to save the world, only to be stopped by Buffy who realized that she, too could close the portal. Dawn continued to stay on with Willow and Tara after Buffy's death and after Buffy's return she lapsed into kleptomania in order to get attention.

Michelle Trachtenberg's television acting career took off with a guest starring role on the Nickelodeon series, The Adventures of Pete and Pete as Nona Mecklenberg. While that series continued, Michelle moved on to daytime soaps as Lily Montgomery on All My Children. While on the show for two years, Michelle worked with her now Buffy co-star, Sarah Michelle Gellar. In 1996, Michelle got her first leading role as Harriet in the Nickelodeon movie, Harriet the Spy.

Her career continued with roles in the TV movies, A Holiday for Love and A Father's Choice, the TV series Meego and was a recurring guest on the Nickelodeon game show, Figure It Out. In 1999, Michelle landed the role of Penny in the movie, Inspector Gadget and co-starred as Julie in Can't Be Heaven. Her latest movie released to theaters was Snow Days. In the summer of 2000, Michelle Trachtenberg got the role of Dawn on Buffy the Vampire Slayer, and is the first character since the show's start to begin as a regular cast member.