Mark Ellsworth Madsen (born January 28, 1976 in Walnut Creek, California) is a basketball player for the NBA's Minnesota Timberwolves. Listed at 6 feet 9 inches (2.06 m) tall, Madsen, who played forward with the Los Angeles Lakers, is a Latter-day Saint and he served a two year mission in Spain on a mission for his church. Because of this, he speaks Spanish fluently. His nickname is "Mad Dog".

After attending San Ramon Valley High School in Danville, California, Madsen played NCAA basketball with Stanford's division one team, and he ranked among the school's all-time leaders in four categories. In addition, he helped the team go to the NCAA tournament each year he spent there, with a Final Four appearance in 1998. He was a two-time All-American and a two-time All-Pac-10.

Madsen was selected by the Los Angeles Lakers in the first round (29th pick overall) of the 2000 NBA Draft. He contributed to the Lakers' world championships in 2001 and 2002. He became an international celebrity for the way he danced at the victory parades for those championships. Pictures of his flamboyant dancing style have been heavily circulated on the internet and has gained a cult-phenomenon status.

Madsen signed with the Timberwolves as a free agent before the start of the 2003-04 NBA season.

As a player, Madsen has become notorious for his practically nonexistent offensive game, which is however balanced by his honest, blue-collar working man's attitude. Madsen has carved out a lasting career in the NBA based on his defense, rebounding, infectious hustle, and locker room presence and regularly gets his playtime.

His lifetime averages are 2.6 points, 2.8 rebounds and 0.5 assists and 13.7 minutes played per game.