Growing up, Mariano Rivera was a shortstop. It's hard to imagine, but the greatest closer of all time did not step on the mound until he was 19 years old. His amateur baseball team in Panama was getting blown out in a playoff game, and despite no experience at the position, Rivera was brought in to replace the team's floundering pitcher. To say he succeeded would be an understatement, as he pitched seven scoreless innings in relief. Two of his teammates then arranged for a local scout for the Yankees to come see Rivera play. After a few more tryouts for the Yankees, the team signed him, adding in a signing bonus of $2,500.
During the 1990 season, his first year in pro ball, Rivera pitched to a 0.17 ERA in 52.0 IP with the Gulf Coast League Yankees as a starter. He was promoted to Low-A in 1991, and posted a 2.75 ERA. His strong strikeout-to-walk ratio (8.29 in 1990) prompted Yankee manager Buck Showalter to state that "this guy is going to make it." Rivera began 1992 in High-A, but suffered an injury to his UCL partway through the season. He went under the knife, though avoided Tommy John surgery. His injury prompted the Yankees to leave him unprotected in the 1992 Expansion Draft, but he wasn't taken by any team. In 1993, he maintained a 2.08 ERA in 43.1 innings, and during the strike-shortened 1994 season, he reached Double-A and Triple-A with a 3.09 ERA in 131 innings.
Rivera made his big-league debut in May 1995, starting four games, but pitching to a 10.20 ERA. He was demoted, and the Yankees started to lose hope in their 25-year-old prospect. That is, until Rivera returned to the minors and his average fastball velocity inexplicably increased to 95-96 from his previous 90 MPH average. When asked to explain how he did this, Rivera stated that it was the work of God. He returned to the majors in July, and pitched primarily as a starter for the team. His incredible work out of the bullpen during the 1995 Division Series convinced the Yankees to convert him to a full-time reliever for the rest of his career.
Results: 61 G, 107.2 IP, 2.09 ERA (240 ERA+), 4.3 fWAR
in 1996, Rivera served as the setup man for established Yankee closer John Wetteland, often pitching both the seventh and eighth innings before turning it over to his fellow lights-out reliever. He broke onto the scene in a big way, posting 130 strikeouts (which was the most by a Yankee reliever in a single season until Dellin Betances struck out 135 batters in 2014) and finishing third in the vote for the Cy Young Award. He even pitched a hidden no-hitter during the year when he had a stretch of 15 consecutive innings pitched without allowing a hit.
Rivera excelled to an even higher level in the 1996 playoffs. In the ALDS against the Rangers, Rivera didn't allow a run in 4.2 innings. After beating the Rangers three games to one, the Yankees went on to face the Orioles. Rivera once again did not allow an earned run in the series, pitching four innings of flawless relief. The Yankees beat the O's four games to one, and advanced to the World Series against the Braves. Unsurprisingly, Rivera pitched incredibly in the World Series as well, pitching 5.2 IP with only one run allowed. He even pitched two scoreless innings in a close Game 6, ultimately preserving the Yankee lead. The team clinched the trophy that night.
What did he do after?
In 1997, Rivera became the team's full-time closer after the Yankees let Wetteland walk as a free agent. Despite blowing nine saves in his first year as closer, the Yankees stuck by Rivera, and their faith in him paid off. He was selected to the All-Star Game that year, the first of his 13 selections. 1997 was also the year that Rivera accidentally stumbled upon the grip for his cutter, which went on to destroy the hopes of batters everywhere.
During the rest of his tenure with the Yankees, Rivera accomplished just about everything. He accrued 652 saves, the most all time. Over the course of his 19-year career, he pitched to a 2.21 ERA (2.76 FIP) and a 204 ERA+, which is first all-time among pitchers who have pitched at least 1,000 innings.
He won five World Series titles (1996, 1997, 1999, 2000, 2009) in addition to being named the World Series MVP in 1999 and the ALCS MVP in 2003. His postseason performance was certifiably insane, as he converted all but five of his 47 postseason save opportunities, pitching to a 0.70 ERA in 141.0 innings overall. That ERA is the best of all time for pitchers with 30 or more innings pitched in the playoffs.
In 2012, Rivera would suffer a devastating injury to his knee while shagging fly balls in the outfield before a game. It ended up being the most serious injury of his major league career and sidelined the ace closer for most of the season. The next year, after returning from injury, he announced that 2013 would be his last. He was greeted with gifts from each team in the league during his "Farewell Tour," culminating in Rivera's final weekend at Yankee Stadium. The team retired his number 42, and on his last night, Joe Girardi removed him with one out left in the game by sending co-members of the "Core Four," Derek Jeter and Andy Pettitte, out to the mound to make the call to the bullpen.
At the end of the 2013 season, Rivera was voted the AL Comeback Player of the Year after he pitched to a 2.11 ERA.
Nowadays, Rivera is mostly involved in philanthropic work both in his native Panama and the United States through his charity, The Mariano Rivera Foundation, which helps provide underprivileged youth with an education. He is a devout Christian, and has helped found churches in both Central America and the U.S.
So, "what did he do after?"–aside from become the greatest closer in baseball history? Oh, not much.