William Perry Jr. (May 31, 1965 – August 7, 2023), better known as DJ Casper (also known as Mr. C The Slide Man), was an American DJ, hype man, and songwriter. Born and raised in Chicago, he was known as "Casper" due to frequently being clad in all white attire on stage.

Perry died of kidney and liver cancer on August 7, 2023, at the age of 58.

In January 2016, Perry was diagnosed with kidney cancer and neuroendocrine cancer.After unsuccessful surgery the same month, he began chemotherapy. In an interview in July 2018, he stated he was in remission. In 2019, Perry stated that he beat his liver and kidney cancers and said he was a changed man, stating "that was God's way of just slowing me down just a little bit."

The "Cha Cha Slide" - also known as the "Casper Slide Pt.1" - was created by Perry for his nephew, who worked as a personal trainer. After the song grew in popularity amongst fitness clubs and Physical Education (PE) in schools as an aerobic exercise, Casper created a second song in 2000, titled "Casper Slide Pt. 2", which was picked up by Elroy Smith at a Chicago radio station. 

The song became a hit in Chicago in 2004, when the city's M.O.B. Records record label became involved as well, helping Perry create a whole compilation album with other Chicago-based artists to promote the dance. "Cha Cha Slide" was later picked up by Universal Records.