Pacheco was born in Tampa and opened a practice in Miami after earning a medical degree from the University of Miami. He met Cassius Clay, who would later become Muhammad Ali, in 1960 when the fighter began training with Angelo Dundee at the 5th Street Gym in Miami Beach.
Pacheco worked as Ali's cornerman from 1962-1977, which included three successful title bouts. Pacheco has said he left his position after suggesting Ali retire because of serious injuries. Ali fought four more matches, losing three.
Pacheco went on to become a television boxing analyst, as well as a painter and author. Pacheco was one of many members of Ali's colorful entourage, traveling the world with the heavyweight champion as he fought the biggest fights of his career. He got a title out of it — "The Fight Doctor" — but Pacheco would later say he never got a penny for his efforts.
His association with Ali did pay off with a gig as a color commentator in network TV fights in the 1980s. By then Ali had been diagnosed with Parkinson's, and Pacheco told about how he tried to get Ali to stop boxing after the brutal "Thrilla in Manila" fight against Joe Frazier in 1975.
Pacheco finally left Ali's camp in 1977 after Ali signed to fight Earnie Shavers. Pacheco would later say that he told Ali he would stick around if he fought boxers who couldn't hurt him, but Shavers was known as a vicious puncher and he feared for Ali's safety.