You would hardly say that Run the Jewels' path to rap stardom is the prototypical plan for a hip-hop superstar. As psychotically youth-obsessed as the hip-hop industry can be, 30-something rap veterans like Killer Mike and El-P do not usually have their pop cultural breakthrough nearly two decades into their careers.

Nor do you typically expect two artists who have so aggressively rejected the accepted tropes of popular rap music as Run the Jewels have to find a true professional renaissance releasing free music on the Internet. None of this has stopped the duo’s second album, Run the Jewels 2, from becoming something approaching a genuine phenomenon. Instantly receiving near unanimous critical praise upon its digital release, the album was reportedly legally downloaded a staggering 150,000 times during the first day according to Rolling Stonean impressive stat for rap’s heavyweights let alone a largely independent rap group.

Meanwhile, the individual paths to stardom for El-P (Jaime Meline) and Killer Mike (Michael Render) have been wildly divergent. ATLien Killer Mike found success as a critically lauded OutKast associate in the early 2000s and won a Grammy before major label intransigence led Mike to pledge his allegiance to the grind of hip-hop independence. In contrast, assuredly New York El-P was a true late-'90s underground hip-hop deity whose brand of music had apocalyptic undertones and aggressively eschewed anything that seemed remotely commercial. A decade and a million war stories later, they became rap music’s most impressive new group.

From the Dungeon Family and Rawkus Records to the Purple Ribbon All-Stars to Definitive Jux, Killer Mike and El-P have produced some of the most celebrated underground (or otherwise) hip-hop ever. Whether you're a newcomer to Run the Jewels or a longtime fan of the pair behind it, here's a listener's guide for the pair’s most essential records over their combined 30-year careers.

B.J. Steiner is a writer living in New York. Follow him @DocZeus.