DJ Mark the 45 King (born Mark James), also known as the 45 King, started DJing in New Jersey in the mid-1980s. The nickname "the 45 King" comes from his ability to make beats using obscure 45 RPM records.

The 45 King first gained fame with his breakbeat track "The 900 Number" in 1987. The song featured a looping baritone sax solo from Marva Whitney's "Unwind Yourself." The 45 King signed with Tuff City Records that year and given a production deal. "The 900 Number" remains his signature work, having been resampled by many artists. He was also featured on the 1989-Hustlers Convention album on the UK label Music of Life, which is considered by many to be hip-hop's first-ever live album.

Using his popularity from the previous release, the 45 King was able to help the other members of his crew, dubbed the Flavor Unit, which included many well-known hip-hop acts including Chill Rob G, Lakim Shabazz, Apache, and Queen Latifah. The 45 King's big break came when Flavor Unit member Queen Latifah was signed to Tommy Boy Records in 1989 (at the time home of De La Soul and Stetsasonic) and released the album All Hail the Queen. The 45 King did extensive production on this album and it is considered by critics to be among his best production work. Over the next few years, many other Flavor Unit members also were signed to Tommy Boy and the 45 King frequently contributed to their albums with his productions.[citation needed]

In the early 1990s, drug addiction took its toll on the 45 King's career, which caused him to lose a production deal that he signed with Warner Bros. Records. Around this time the 45 King released multiple series of breakbeat records (the Lost Breakbeat series, the Breakapalooza series, etc.) and a few tracks for other MCs, but he stayed mainly with his breakbeat record franchises.

In July 1990, Manchester-born DJ Chad Jackson sampled "The 900 Number" on his single "Hear the Drummer (Get Wicked)," which reached #3 in the UK Charts. A remixed version was also a minor UK hit in 2007. Jackson was apparently unaware that the song had itself been sampled from the original "Unwind Yourself" as he creditted himself and King as co-writers of the song

In 1996, Washington, D.C.-based go-go artist DJ DJ Kool scored a big hit with the song "Let Me Clear My Throat." It was simply call-and-response vocals over a chopped half of the "900 Number" beat, but it was popular nationwide. DJ Kool did not just sample the track, he acknowledged the 45 King's as the song's originator, and the 45 King even remixed the track for Kool.

In 1998, the 45 King produced "Hard Knock Life (Ghetto Anthem)" for Jay-Z. The song was a hit that featured a looped chorus from the Broadway Musical Annie. In 2000, he produced the platinum track "Stan" for Eminem, solidifying his reputation as a celebrated hip-hop producer.

Currently, the 45 King is supposedly working on a solo project, a compilation of emcees over his beats.