Prior to the acquisition, a famous - and now deleted - video featured singer-songwriter Tyrese Gibson describe Dr. Dre - whose real name is Andre Romelle Young - as "the first billionaire in hip-hop right here".
But although he's not quite there, pre-tax earnings of $620 million mean he's well on his way. His sizeable fortune outstripped that of all remaining 24 "Cash Kings" combined.
With $60 million each, Jay-Z and P-Diddy took joint second place, but were left trailing behind the Beats co-founder.
Shrewd businessmen Jay-Z has an impressive portfolio, which includes the Roc Nation entertainment empire, a stash of concert dates, his D'Usse Cognac costing around $50 a bottle and new album Magna Carta Holy Grail.
Read More Apple to shut down Beats Music: Report
An agreement with Diageo's Ciroc vodka drove most of the earnings of P Diddy - real name Sean Combs - which also got a boost from DeLeon tequila, Blue Flame marketing agency, Sean Jean clothing and Revolt TV.
Canadian rapper and songwriter Drake came in fourth place with an impressive $33 million. His album Nothing Was The Same, an arena tour and endorsement deal with Nike's Jordan line meant his earnings tripled in a year.
Macklemore and Ryan Lewis, who took the title of Best New Artist at this year's grammy awards, came fifth after amassing earnings of $32 million.
Other rich rappers include Kanye West in sixth place ($30 million), Cash Money co-chief Birdman in seventh place ($24 million) and Lil Wayne ($23 million) in eighth place.