This is pretty fascinating stuff right here, this article from Flavorwire on 78 things you didn't know about Johnny Cash. For instance:
31. The camper Cash used for his amphetamine binges in the desert was named Jesse James. It had its windows spray-painted black so Cash could sleep during daylight hours, “but also because I just liked to spray-paint things black.” 32. After an oil leak from Jesse James set the Los Padres National Wildlife Refuge on fire, Cash became the only person ever successfully sued by the U.S. for starting a forest fire. 39. President Jimmy Carter was June Carter’s cousin, related to Cash by marriage. 40. Cash was also distantly related to King Duff, the first king of Scotland. 53. The tune for “I Walk the Line” was inspired by a recording of Bavarian guitar music Cash had accidentally played backwards.
And don't miss the Elvis impersonation referenced in #14: