The R was on my mind this morning

Maybe it was listening to that sick Funk Flex 4th of July mix.
The R may be Hip-Hop's Coltrane.

From wiki-wiki-wiki-wiki

In 1985 he formed a musical partnership. Eric B. and Rakim subsequently became one of the most well-known and influential groups in hip hop history. Prior to Rakim's arrival on the scene, hip hop rhyming still exhibited strong ties to rapping's roots in improvisatory toasting, in very regular meter and rhyme scheme (Run DMC, Kurtis Blow, and others), with simple lyrics and a steady and heavily prounounced rhythm. Rakim, in contrast, says he tried to model his flow after the saxophone's instrumentation in a jazz song. The All Music Guide's Steve Huey wrote in the early 2000s that "Rakim's flow is smooth and liquid, inflected with jazz rhythms and carried off with an effortless cool that makes it sound as though he's not even breaking a sweat. He raised the bar for MC technique higher than it had ever been".