Mariano Rivera (Mo) has been closing games for the New York Yankees since 1996. Racking up 649 saves with a career era of 2.21, he's the best closer in the history of MLB. Mo's dominance doesn't only reside in the regular season, but in the post season Mo has pitched to the tune of 42 saves and a remarkable .70 era. What makes Mo's career that much more impressive is that he's done all of this with just one pitch. The cut fastball. When his cut fastball is working (and it rarely isn't) it's as unhittable as it gets. While other closers have 95+ mph fastballs Mo gets it done with his cutter.
Considering that Mo has gone above and beyond for the Yankees all these years he's earned the right to say when he wants to retire and he's said that this is going to be his last year in the majors. As is custom in MLB when a specific player has decided to retire other teams offer gifts of appreciation to said player. When Mo had his final game in Minnesota the Twins gave Mo a rocking chair made of broken bats (which is part of what makes Mo's cutter so devious because it has the potential to shatter any bat). So as Mo's goodbye tour continues more and more teams are showing the legend respect with standing ovations and the such.
Imagine being Mo's manager, you would obviously want to keep Mo at the back end of your bullpen until he can't even walk anymore, but cut it out. Don't try to "talk" Mo into staying he's decided he's done let him ride off into the sunset and end his career. The Yankees have his replacement in David Robertson let him come into Spring Training knowing he's the main option at closer and not have to worry about the shadow of Mo hovering over him; Mo isn't Brett Favre.