Hilary Erhard Duff (born September 28, 1987) is an American actress, businesswoman, singer, songwriter, producer, and writer. Duff began her acting career at a young age and quickly became labeled a teen idol as the title character of the television series Lizzie McGuire (2001–2004) and in the theatrical film based on the series, The Lizzie McGuire Movie (2003). Thereafter, she appeared in numerous films, with leading roles in Cadet Kelly (2002), Agent Cody Banks (2003), Cheaper by the Dozen (2003), A Cinderella Story (2004), and Cheaper by the Dozen 2 (2005). She later began appearing in independent films playing a wider range of roles, such as a promiscuous popstar in War, Inc. (2008), a suicidal and rebellious teenager in According to Greta (2009), and as the dramatic title character in the controversial The Haunting of Sharon Tate (2019). She has also executive produced several of the projects she starred in, such as According to Greta, Beauty and the Briefcase (2010) and The Haunting of Sharon Tate. From 2015 until 2021, she starred as Kelsey Peters on TV Land's longest-running original 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). The latter earned her acclaim for experimenting with dance music, despite the unpopularity of the genre at the time. 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 five positions in her major markets: the US and Canada. In addition to music and acting, she 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).
Duff's success in the entertainment industry led her to venture into business with fashion lines of her own such as Stuff by Hilary Duff, Femme for DKNY, and most recently the "Muse x Hilary Duff" collection, a collaborative effort with GlassesUSA which was credited to have boosted GlassesUSA's sales for its premium brands. She has also invested in a number of businesses ranging from cosmetics to children's products. In 2019, she was appointed as the chief brand officer of Naturalena Brands' "Happy Little Camper" and "Veeda" lines of products. Duff has been the subject of media attention throughout her career, with interest focusing on her romantic relationships and public image, especially her relationships with Aaron Carter and Joel Madden when she was a teenager. Duff has been married twice, firstly to former professional ice hockey player Mike Comrie from 2010 till 2016, and later to record producer and singer-songwriter Matthew Koma since 2019. Duff has also been hailed as 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.