He might have retired at one stage but US rap superstar Jay-Z is officially the wealthiest rapper of all time, according to influential US magazine Forbes.

The 37-year-old star, who's set to release new LP American Gangster later this year, beat out 50 Cent for the top spot, and said the cash is good but not important.

"There's one thing in the world money can't buy," Jay-Z pointed out, "and that's cool. Now I have all the cool things that a lot of hard work has created for me. If I'm the king, ain't nobody gonna take this crown away from me."

Jay-Z is valued at almost AU$38 million.