The reason Pacquiao has had such longevity and was atop most pound-for-pound best boxer lists for a good portion of his career has been his willingness to go out and fight the best fighters who were willing to fight him.
That list includes an unbelievable 22 world champions: Chatchai Sasakul, Lehlohonolo Ledwaba, Jorge Eliecer Julio, Marco Antonio Barrera (twice), Erik Morales (twice), Oscar Larios, Jorge Solis, Juan Manuel Marquez (twice), David Diaz, Oscar De La Hoya, Ricky Hatton,Miguel Cotto, Joshua Clottey, Antonio Margarito, Shane Mosley, Brandon Rios, Timothy Bradley (twice), Chris Algieri, Jessie Vargas, Lucas Matthysse, Adrien Broner and Keith Thurman.
That’s a lot of fighters who, at one point in their careers, could say they were the best.
Words to remember: "If Pacquiao decides to hang up the gloves while he's still on top, then very few fighters in the sport's history can claim a better legacy. BoxRec ranked Pacquiao second all-time in the pound-for-pound division behind only Floyd Mayweather Jr., who retired with a perfect 50-0-0 record. ESPN.com also ranked Pacquiao second among pound-for-pound fighters in the past 25 years, behind only Mayweather. Among many accolades, the Boxing Writers Association of America named Pacquiao the Fighter of the Decade in 2010. The Ring and the BWAA also named him the Boxer of the Year three times. The southpaw has defeated some of boxing's best fighters during his time, including Oscar De La Hoya, Miguel Cotto, Juan Manuel Marquez, Ricky Hatton, Erik Morales and Thurman. Pac-Man's in-ring legacy can only be matched by perhaps Mayweather or Muhammad Ali." — Bleacher Report, 2019