Two Hells Angels and one Mongols member died as bikers brawled and gunfire erupted. Casino patrons and bikers dove for cover behind blinking slot machines. More than a dozen people were hurt.

For Hells Angels bikers, "81" is not just some random number. It represents the Hells Angels brand and can be used by those ...

(Robert Altman/Michael Ochs Archives/Getty Images) In 2011, the U.S. Department of Justice said the Hells Angels had as many as 2,500 members in 230 chapters in 26 countries.