BOSTON -- David Ortiz's fame has been built on some of the most important hits in the history of the Boston Red Sox, one of the most storied franchises in professional sports in the United States. But saving lives is one of the most important and least recognized aspects in the career of the star from the Dominican Republic, who is affectionately known as "Big Papi."

Ortiz, who is retiring from baseball at the end of this season, is one of the best designated hitters of all time and one of the most productive hitters of his era. Ortiz is one of four players to notch 600 doubles and 500 home runs in their careers and is the all-time leader in games, hits, doubles, home runs, runs, RBIs, walks and total bases among designated hitters.

He was selected to 10 All-Star Games, regularly received the Silver Slugger, won three championships and was named ALCS MVP in 2004 and World Series MVP in 2013. He has hit 11 walk-off home runs and 11 grand slams in the regular season and started this year's playoffs with 17 homers and 60 RBIs in the postseason.

In his last season, the 40-year-old is one of the leading candidates for the American League MVP and Hank Aaron awards thanks to his great performances on the field. But those numbers and accomplishments have taken a back seat in the player's order of priorities since February 2005, when he decided to create the David Ortiz Children's Fund with the sole purpose of saving children with heart problems.

“I want to be remembered not as someone who just looked after himself, but as someone who tried to do his bit to make a difference,” Ortiz told ESPNDeportes.com. “There's no hit, achievement, title or award that can compare with the enormous satisfaction of giving a child their smile back.”

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Since it was founded, the David Ortiz Children's Fund has raised nearly $3 million and funded heart surgery for hundreds of children from the Dominican Republic and the New England area. The majority of these children come from families without resources or access to the medical services needed to save their lives.

In partnership with the Massachusetts General Hospital For Children in Boston and the World Pediatric Project organization, Big Papi hosts the David Ortiz Celebrity Golf Classic every December in Punta Cana, Dominican Republic, in which MLB stars participate alongside stars from other sports and the world of show business.

Last year, in which 70 children underwent surgery, a Dominican hospital named its pediatric department after Ortiz, and the newspaper Diario Libre named him Man of the Year. During the final weekend of this year's regular season in Boston, the Red Sox presented him with a number of gifts, including donating $1 million to his fund.

David Ortiz and the Boston Red Sox were eliminated from postseason play by the Cleveland Indians. Billie Weiss/Boston Red Sox/Getty Images

“Saving lives is unique in the world, and I've had the opportunity, thanks to a working group, to provide surgery for kids and give them back their nature, by the great power of God,” Ortiz said.

“There are times I have bad games, there are times when I'm in a slump, there are years when we lose [more games than we win], but during that time there are times when they call me and tell me that they operated on 15 children and that everything went well,” said the Red Sox legend.

“They say ´look, here are photos, videos, the family thanks you.' And [when that happens] it makes me forget how badly things are going on the field, because things happen on another level and, for me, that's important,” he said.

Of course, regularly hitting the ball out of the park has been a basic ingredient for the success of Ortiz's fund.

“I'm not going to lie, all this has happened thanks to what I do on the field. The Big Papi product is a package where one thing complements the other,” Ortiz said.

“Many people won't believe this, but my son has always cared about other people ever since he was just a kid,” said Big Papi's father, Leo Ortiz, at Fenway Park.

“When he was 13, he showed his generosity towards others. I took him for breakfast before going to the stadium and he invited kids I didn't know and that he knew couldn't afford to pay for food. He just invited them and told them 'don't worry, my old man will pay,' without asking me beforehand whether I had the money to cover it,” said the elder Ortiz.

“God has given me much more than I deserve and the most logical way of thanking him is by helping others. Acting as a channel to help save lives and bring joy to children and their families,” Ortiz said. “There can be no greater happiness."

Read the original Spanish-language version of this story here.