Though many are convinced it won't stick, mixed martial arts star Conor McGregor announced his retirement on Sunday. McGregor tweeted, "Hey guys I’ve decided to retire from fighting. Thank you all for the amazing memories! What a ride it’s been!" McGregor, age 31, has announced his retirement at least once before. If this is really it, McGregor walks away with an MMA career mark of 22-4, including UFC championships in two weight classes. In boxing, McGregor is 0-1, the sole bout being a 2017 pay-per-view fight against Floyd Mayweather which he lost by tenth-round stoppage. McGregor earned a reported $130 million for that fight, which gives him a unique boxing record: most money earned per boxing match.