The best closer in the history of baseball will be calling it a career at the end of the 2013 season.

Mariano Rivera has had quite a run with the New York Yankees. The five-time World Series champion will leave the game of baseball with over 600 career saves, more than 1,000 appearances with the Yankees, and the most seasons with at least 30 saves. And that's just the regular season.

Rivera towers over everyone else at his position, and it's very possible that the sport will never see another approach the standard he set.It's important to remember that what Rivera mainly does—pitch one inning a night when his team has the lead—is still a fairly new role. In the future, the role of the closer may change once again.