Cintron had a tough childhood. He witnessed as his mother lay in bed for months before she died of Cancer. Unable to care for Cintron and his siblings, Cintron's father sent him to the United States, with Cintron's uncle, Benjamin Serrano, a former Middleweight contender who had fought Frank The Animal Fletcher among others. Cintron's father, however, kept regular contact with his kids. But when Cintron was 13, another tragic blow shaked him: His father died of a heart attack, leaving him and his siblings orphaned on both sides.
Cintron found wrestling and boxing to be an outlet from his personal troubles, so he started spending more and more of his time practicing those sports. He became an accomplished high-school wrestler, but an injury to his knee prevented him from going on. Because of that, he turned into boxing full time.
However, he did not start boxing in the amateurs until he was 19. He compiled a record of 24 wins and 3 losses as an amateur.
On the night of October 7, 2000, he knocked out Jesse Williams in two rounds in Lancaster to begin his professional career. With that, he began an undefeated streak that has continued on.
One of his toughest tests so far came against Omar Davila, February 16 of 2002. He took up the fight on one week's notice and travelled to San Antonio, to fight at his opponent's hometown. Cintron was cut on the side of one of his eyes in round one. Facing adversity, he came back to defeat Davila by knockout in round two.
Cintron was featured on NBC May 18 of 2003, against Puerto Rican veteran Luis Rosario, and he won by knockout, 59 seconds into round one.
KO Magazine made a feature article on Cintron, where they compared him to Felix Trinidad and Thomas Hearns.
He has a record of 19 wins without losses, with 18 wins by knockout