I've been toying with the idea of a Men in Black/Johnny Cash crossover recently, but then decided i'd follow the recent trend in Hollywood of re-imagining historical figures and fictional characters as action heroes. For example Abraham Lincoln: Vampire Hunter, Hansel & Gretel: Witch Hunters and Sherlock Holmes to name but a few.
After the Roswell incident the American Government enlisted Johnny Cash to assist the CIA in hunting and neutralising alien threats, in doing so he became the original Man in Black. The many unusual events in Johnny's life were often cover ups for his top secret field work, including the seven nights he supposedly spent in jail.
Although the public remained oblivious to most of his missions, there were occasions when the existence of aliens was almost revealed to the public. One such occasion forced Johnny to burn several hundred acres of Los Padres National Forest in order to remove all traces of the events that transpired in the hours beforehand.