The “motorcycle gang” as we know it—formally organized groups of hell-raising hog-riders who live on the edge of the law—first appeared in the 1940s, as part of the big post-World War II club-forming craze in America. They existed in opposition to legacy motorcycle clubs, groups of good citizens who cut their hair and followed the rules of the road. According to a 1991 report from the California Department of Justice, the first schism in Motorcycle Nation happened in 1947, when a rowdy group called the Pissed Off Bastards of Bloomington “turned the American Motorcycle Association- (AMA) sponsored Hill Climb into a week-long brawl.” The next year, after a motorcycle riot in Riverside, Calif., the local police chief pinned the violence on out-of-town “outlaws.” The name stuck.

The most notorious outlaw motorcycle gang is, of course, the Hells Angels—itself a spinoff of the Pissed Off Bastards of Bloomington—the roughnecks perhaps best known for doing a very bad job providing security at the Altamont Free Concert. Other prominent gangs include the Outlaws, the Bandidos, the Pagans, the Mongols, and the Vagos Motorcycle Club. Though they may have all begun as groups of motorcycle enthusiasts who consolidated to protect their rights to wear scraggly beards and drive like jerks, authorities believe they eventually diversified into more serious criminal activity.