Holly Madison (born Hollin Sue Cullen; December 23, 1979) is an American television personality, actress and model best known as a former girlfriend of Hugh Hefner and for her appearance in the reality television show The Girls Next Door. She also starred in her own reality series, Holly's World, which ran from 2009 to 2011. She has released two books, Down the Rabbit Hole in 2015, about her life in the Playboy Mansion and her relationship with Hefner, and The Vegas Diaries: Romance, Rolling the Dice, and the Road to Reinvention in 2016.

Madison was born Hollin Sue Cullen in Astoria, Oregon. At age two, she moved with her family to Craig, Alaska, on Prince of Wales Island. When she was in middle school, her family returned to St. Helens, Oregon. She later attended Portland State University for two years, majoring in theater and psychology. Afterward, Madison moved to Los Angeles and attended Loyola Marymount University.

To afford her college tuition, Madison competed to become a Hawaiian Tropic model and worked as a waitress at Hooters. Her appearance at those venues led to invitations to the Playboy Mansion and, at the age of 21, after more than a year of such visits, Madison asked permission from Hugh Hefner and was eventually allowed to move in at the mansion.

Facing credit card debt and potential homelessness, in August 2001, Madison moved into the Playboy Mansion and officially became one of Hugh Hefner's girlfriends. Hefner controlled her finances, enforced a strict schedule and curfew, and denied her opportunities to earn income outside the mansion. In February 2002, after all but two of his girlfriends left, Madison became his "#1 Girl". During her time with Hefner, Madison stated that she wanted to marry him and have his children. However, in an interview at the Playmate of the Year luncheon in May 2008, Hefner said, "I love Holly very much and I think we're going to be together the rest of my life, but marriage isn't part of my puzzle. It's not a personal thing; I just haven't had much luck with marriages." Reflecting on her time at the mansion, Madison claimed that her feelings for Hefner were attributable to Stockholm syndrome.

On October 7, 2008, Madison announced that her relationship with Hefner had ended, but that she, Bridget Marquardt and Kendra Wilkinson were "still filming stuff together". Hefner confirmed the breakup, saying, "If Holly says it's over, I guess it's over". Madison was later among the former Playmates who spoke out in the docuseries Secrets of Playboy.

The Girls Next Door was an E! Network show following life of Madison and others at the Playboy Mansion. Although Madison was never a Playboy Playmate, Playboy published a nude pictorial of Madison with her The Girls Next Door costars in the November 2005 issue. The women were featured again on the covers of the September 2006, March 2008, and February 2009 issues. During seasons three and four, Madison was shown working at the Playboy studios as an intern and later a junior photo editor. She also helped design and put together The Girls Next Door calendars. In February 2009, with the ending of the sixth season she quit working for the company altogether due to her split from Hefner making her position "awkward".

Madison was chosen to replace Jewel on season 8 of Dancing with the Stars and was partnered with Dmitry Chaplin. She and Chaplin were voted off in a double elimination, ultimately placing 11th.

In May 2009, Madison and Las Vegas Mayor Oscar Goodman led a Guinness World Record-breaking "largest bikini parade ever". According to the Las Vegas Sun, "The politician and the former Playboy house bunny joined forces to usher in the city's summer swimsuit season..." in an event timed to coincide with the 50th anniversary of the Welcome to Fabulous Las Vegas sign. The 281 parade participants broke the prior record of 250. The mark has subsequently been eclipsed by events in the Cayman Islands (331), and Brisbane, Australia (357).