In the late '70s, Andy Gill and Jon Langford were schoolmates at the University of Leeds in England. That was where Andy co-founded a band called Gang of Four and Jon helped start a band called the Mekons. Those bands went on to great things, such as helping to invent post-punk — and becoming iconic bands in the process.

The Mekons are possibly the longest-running and certainly the most beloved post-punk band. Their music has encompassed punk rock, country music and dub reggae, and they've released a long string of truly great albums like Fear and Whiskey (1985) and The Mekons Rock & Roll (1989). Their history, their music and their perseverance through thick and thin, not to mention their sense of humor, are showcased in the 2015 documentary Revenge of the Mekons.

In the late '70s and early '80s, Gang of Four made some classic albums of life-changing, canonical Neo-Marxist post-punk, like Entertainment (1979), Solid Gold (1981) and Songs of the Free (1982). They've influenced everybody from Rage Against the Machine to St. Vincent. With Andy Gill as the sole remaining original member, they released an album in 2015 called What Happens Next.

Here, these two smart musicians and old friends recall their common roots, trace the evolution of the concept of punk rock as it traveled north through England, and how it inspired their respective bands.

Punk's chief message, according to these guys: "You can really go anywhere you want with it."