Rapper Jay-Z had the childhood nickname “Jazzy,” and also grew up near the J/Z subway station in New York, so adopted that musical name (he was born Shawn Carter).
Electronic musician Moby’s late father gave him that nickname because Moby is the great, great, grandnephew of Herman Melville, author of the classic novel Moby Dick (born Richard Melville Hall).
Rapper Eminem is just using his initials; he was born Marshall Mathers III.
Public Enemy’s Chuck D is shortening his real name, Carlton Douglas Riddenhour.
The Beastie Boys’ stage names are related to their birth names: Mike D was born Michael Diamond, Ad-Rock is Adam (Horowitz) and MCA is short for MC Adam (Yauch).
Notorious B.I.G., aka Biggie, was indeed a large man. Born Christopher Wallace, his autopsy reported that he was 6’2″ and 395 lbs. when he died at age 24.
Run-DMC was named for Joseph Simmons’ earlier DJ name, DJ Run, and the D and Mc of member Darryl McDaniels. The other member was Jam Master Jay, born Jason Mizzel.