That would be rookie reliever Kenley Jansen, who set a Major League record by striking out a staggering 16.1 batters per nine innings (with a minimum of 50 innings). Jansen fanned 96 in 53 2/3 innings, raising the bar from the 15.99 mark set by Cubs closer Carlos Marmol last year.
"And I had an 11.45 ERA in April," Jansen points out with equal parts pride and astonishment, a splashy 2.85 ERA at the finish underscoring an in-season transformation almost as remarkable as the one he made two years ago when he went from catcher to pitcher.
Jansen, who turned 24 last week, leaped over some pretty impressive Dodgers relievers as a one-season strikeout machine, closers like Cy Young Award winner Eric Gagne (14.98) and All-Stars Jonathan Broxton (13.50) and Takashi Saito (12.29).
Jansen credits a drill overseen by bullpen coach Ken Howell and bullpen catcher Mike Borzello for the breakthrough in his command. Before each game, Jansen would throw a 15-pitch bullpen session working on hitting specific locations.
"My command wasn't good enough," said Jansen. "Then it really clicked. I straight-up remember the very first pitch and my focus was better. I was throwing through the catcher's glove, not to it. Focusing on strike one.
"This has been awesome. Growing up as a kid, you dream of just playing in the big leagues. And here you are, you're pitching in big league games, and the next thing you know you've got an all-time record? It's amazing."
Of course, Borzello sort of tipped the hand on Jansen in Spring Training, when he mentioned that Jansen's cutter had the natural wickedness of another reliever he was pretty familiar with, a reliever who coincidentally was already Jansen's idol and role model.
The pitch he compared it to was all-time saves leader Mariano Rivera's cutter -- basically his only pitch -- which Rivera developed by accident after he had already been promoted to Major League closer in 1997. The Yankees even tried to get Rivera back to throwing the straight fastball, but abandoned the effort when his cutter turned out to be tougher to hit.
Nobody outside of Jorge Posada has caught more Rivera pitches than Borzello, who for more than a decade was the Yankees' bullpen catcher. He was catching Rivera when that cutter inexplicably appeared.
"Mariano can pinpoint that pitch now, but not at the beginning," said Borzello. "Kenley's pitch has the same action."
Jansen, a native of Curacao and Little League teammate of Atlanta's Jair Jurrjens, gained notoriety for throwing out basestealers from his knees during the World Baseball Classic two years ago, but was converted from a weak-hitting catcher to the mound during that 2009 season.
He opened the 2010 season in Class A and ended it closing games in the Major Leagues, dominating at Double-A Chattanooga in between and saving the Double-A Southern League All-Star Game. He earned a save in his second Major League appearance and four in 25 games in 2010. Rivera didn't get his first save until he was 26. Jansen struck out 41 with 15 walks in 27 innings, and his 0.67 ERA was the fourth lowest by a rookie with a minimum of 25 innings in Major League history.
Jansen's 2011 season was interrupted three times -- he was optioned at the beginning of May to make room for the activation of Hong-Chih Kuo, disabled at the end of May when he tried to pitch through shoulder inflammation and disabled in mid-June with an irregular heartbeat.
Nonetheless, in his last 31 2/3 innings, Jansen allowed only nine hits in 102 at-bats (.088), and he saved five of six opportunities on the season. In September, Jansen struck out 32 and walked only three.
Manager Don Mattingly said Javy Guerra, who converted 21 of 23 save opportunities this year, deserves to be the closer coming into 2012. But it's hard to imagine Jansen not being a closer if he keeps up his dominating ways.
"He came into camp, and all of a sudden there were expectations, and I didn't think he dealt with that early on," said Mattingly. "He went to the Minor Leagues and worked on his game, improving his command and holding the running game better.
"Now, I feel I can count on him. He's going into the winter with a whole new mindset. He knows he belongs. He'll walk into that clubhouse in the spring knowing he's a big league player."
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.