Hilary Erhard Duff (born September 28, 1987) is an American actress, businesswoman, singer, songwriter, and writer. Duff began her acting career at a young age and quickly became labeled a teen idol as the title character of the hit television series Lizzie McGuire (2001–2004) and in the theatrical film based on the series, The Lizzie McGuire Movie (2003). Thereafter, Duff appeared in numerous films, with leading roles in Agent Cody Banks (2003), Cheaper by the Dozen (2003), A Cinderella Story (2004), and Cheaper by the Dozen 2 (2005). After experiencing commercial and critical failure in Material Girls (2006), Duff began appearing in independent films such as War, Inc. (2008), According to Greta (2009), and The Haunting of Sharon Tate (2019). She was also an executive producer on the latter two films. Since 2015, she has starred as Kelsey Peters on the TV Land comedy-drama series Younger, for which she has received nominations for People's Choice Awards in 2016 and 2017.
Duff first came to prominence in music after releasing her Christmas-themed debut studio album, Santa Claus Lane (2002), through Walt Disney Records. She then enjoyed significant commercial success and platinum and gold certifications with her subsequent studio albums released through Hollywood Records, including Metamorphosis (2003), Hilary Duff (2004), Most Wanted (2005), and Dignity (2007). Following a hiatus from music, Duff signed with RCA Records for her fifth studio album, Breathe In. Breathe Out. (2015), which debuted in the top 5 positions in Duff's major markets: the US and Canada. In addition to music and acting, Duff has also co-authored a trilogy of novels, beginning with Elixir (2010), which became a New York Times best seller, and followed by the sequels Devoted (2011) and True (2013).
Her success in the entertainment industry led her to venture into business with fashion lines of her own such as Stuff by Duff, Femme for DKNY, and most recently the "Muse x Hilary Duff" collection, a collaborative effort with GlassesUSA. She has also invested in a number of businesses ranging from cosmetics to children products. She has been the subject of media attention throughout her career, with interest focusing on her romantic relationships, friendships, and public image, especially her relationships with Aaron Carter and Joel Madden when she was a teenager. Duff was married to Canadian former professional hockey player Mike Comrie from 2010 to 2016, with whom she shares a son. She is engaged to musician and music producer Matthew Koma, who shares a daughter with her. Duff was an inspiration by subsequent Disney teen stars such as Miley Cyrus, Demi Lovato, Bridgit Mendler, and Selena Gomez and has sold an estimated 15 million records since her debut in 2002.
She is also known as Hilary Erhard Duff and Hillary Duff.