Manny Pacquiao has now won world titles in 4 different weight groups. How many other fighters have done this?

Question

And how many have won in 5 or more?

Answer 1

Mayweather.  It is a lot easier to do it at the lower weight classes.  You can take more fights and train more rigorously because the training takes less of a toll on your body.

Answer 2

Here is a list of fighters that won world titles in 4 different weight divisions:

Pernell Whitaker:

~2/19/1989- wins a lightweight world title.

~7/18/1992- wins a junior welterweight world title.

~3/6/1993- wins a welterweight world title.

~3/4/1995- wins a junior middleweight world title.

Roberto Duran:

~6/26/1972- wins a lightweight world title.

~6/20/1980- wins a welterweight world title.

~6/16/1983- wins a junior middleweight world title.

~2/24/1989- wins a middleweight world title.

Roy Jones, Jr.:

~5/22/1993- wins a middleweight world title.

~11/18/1994- wins a super middleweight world title.

~8/7/1997- wins a light heavyweight world title.

~3/1/2003- wins a heavyweight world title.

Here is a list of fighters that have won world title is 5 different weight divisions (De La Hoya won in 6):

Oscar De La Hoya:

~3/5/1994- wins a super featherweight world title.

~7/29/1994- wins a lightweight world title.

~6/7/1996- wins a junior welterweight world title.

~4/12/1997- wins a welterweight world title.

~6/23/2001- wins a junior middleweight world title.

~6/5/2004-wins a middleweight world title.

Floyd Mayweather, Jr.:

~10/3/1998- wins a super featherweight world title.

~4/20/2002- wins a lightweight world title.

~6/25/2005- wins a junior welterweight world title.

~4/8/2006- wins a welterweight world title.

~5/5/2007- wins a junior middleweight world title.

Thomas Hearns:

~8/2/1980- wins a welterweight world title.

~12/3/1982- wins a junior middleweight world title.

~3/7/1987- wins a light heavyweigh world title.

~10/29/1987- wins a middleweight world title.

~11/4/1988- wins a super middleweight world title.

Sugar Ray Leonard:

~11/30/1979- wins a welterweight world title.

~6/25/1981- wins a junior middleweight world title.

~4/6/1987- wins a middleweight world title.

~11/7/1988- wins a super middleweight world title.

~11/7/1988- wins a light heavyweight world title (won it the same night as 168 lb title).

Manny Pacquiao:

~12/4/1998- wins a flyweight world title.

~6/23/2001- wins a junior featherweight world title.

~11/15/2003- wins a featherweight world title.

~3/15/2008- wins a super featherweight world title.

~6/28/2008- wins a lightweight world title.

NOTE: I include Manny for 5 divisions because when he beat Marco Antonio Barrera, he won the linear and Ring Magazine championship.  Some people don't include that win as a world title victory because there was no sanctioning body's belt on the line (WBA, WBC, IBF, WBO), but I include it because the Ring Magazine belt is more important and respected than any of the sanctioning bodies, and Barrera was considered by everybody to be the true champion and best fighter in the featherweight division at that time.