Harvey Walden IV (born December 21, 1966) is a former United States Marine drill instructor, author, actor and television host.

He is best-known in the U.K. and U.S. for scaring the living daylights out of over-weight celebrities and contestants in ITV's and VH1's Celebrity Fit Club as the no-nonsense expert fitness instructor. He joined the U.S. Marines aged 17 and completed his Basic Military Marine training (also referred to as `Boot Camp') at MCRD San Diego, CA. He was a Drill Instructor at MCRD Parris Island, SC. He is a weapons expert and has black belts for various types of martial arts.