For years, deciding the pound for pound king of boxing was a pretty basic binary question: Mayweather or Pacquiao? Then, Juan Manuel Marquez flattened Pacquiao and there was no more debate to be had. When Floyd Mayweather retired in 2015, that title of pound for pound champion became disputed once again, and it remains that way today.
Roman Chocolatito Gonzalez was #1 on many lists (mine included) after Floyd, but back to back losses to Srisaket Sor Rungvisai have definitively ended that run. Andre Ward seemed to be the clear pick after his defeats of Sergey Kovalev, but now Ward too is retired.