Hip hop legend Rick Rubin has a way with music and words -- he launched Def Jam, after all -- but when it comes to his own name he needs a little help from a judge ... to change it.
Rubin's filed legal docs -- obtained by TMZ -- to legally change his name from the one on his birth certificate ... Frederick Jay Rubin.
The famed producer -- who's worked with Jay Z, the Beastie Boys, Metallica, Neil Diamond and many many more -- simply wants to make his nickname all legal and stuff.
Yes, he's going from Frederick to Rick -- 'cause who'd work with Fred Rubin?
As for why 51-year-old FredeRick's making the dramatic change -- his rep had no comment.