Sam was the owner and head bartender of Cheers.
Sam "MayDay" Malone was an erratic relief pitcher for the Boston Red Sox, reaching the highest of highs (saving both ends of a double header), and the lowest of lows (beaning the Orioles mascot while in a drunken stupor). His reputation as a ladies' man and hard drinker still made him a fan favorite, of sorts, even after his growing alcoholism forced him out of the game. Eventually, he kicked his drinking habit, and found himself as the owner/head bartender of Cheers.
Though he wasn't drinking anymore, he still could have any woman he wanted. And he pretty much did have every woman, until Diane Chambers arrived. After giving her a job out of pity, he was drawn to her education, as well as her constant rejection of his advances, and eventually she gave in, resulting in a passionate but volitale relationship that lasted for several years (through several breakups). After a lengthy conflict over the process, Sam and Diane were finally engaged, but shortly after Diane left for a few months to work on a book, but Sam correctly predicted that she wouldn't return.
Sam was deeply affected by Diane's departure, so he sold the bar to a huge corporation and bought a boat, hoping to spend a leisurely life at sea. But after only a few months it sunk, so he returned to Cheers, tending bar under the supervision of new manager Rebecca Howe. Sam was instantly attracted to Rebecca, but she was a businesswoman with her sights set on successful businessmen, with no time for a workingman like Sam. He eventually grew frustrated at working for someone else, and set his sights on owning Cheers again. It was a struggle, but he eventually was able to buy back the bar, retaining Rebecca as a manager of sorts.
As Sam grew older, he began to feel some regret about his promiscuous lifestile. At the suggestion of Frasier, he began seeking treatment for sexual compulsion. He and Rebecca tried having a baby together.
Through all of this, Sam was always trying to recapture his former glory. Though he was still adored by the gang at Cheers, he longed for the love of the fans and the thrill of competition. He tried commercial acting, sportscasting, and charity sports events to reconnect with the fans, and was constantly competing with everyone, from his friends and coworkers to the staff of a rival bar, Gary's Olde Towne Tavern.
In line with the Cheers finale, Sports Illustrated featured an article about Sam's baseball career, including career stats and several doctored photos of MayDay in action.