The first boxer to win world titles in three or more different weight classes was Henry Armstrong. Armstrong, a professional boxer from the United States, achieved this remarkable feat during his career in the 1930s and 1940s. He won the world titles in the featherweight (126 lbs), lightweight (135 lbs), and welterweight (147 lbs) divisions, becoming the first fighter to accomplish this feat. Armstrong's ability to compete and succeed across multiple weight classes solidified his legacy as one of the greatest boxers in history.