Who is the only boxer to hold world championships in three weight classes simultaneously?

Henry Armstrong was the only boxer to hold world championships in three weight classes simultaneously.

Armstrong achieved this remarkable feat in 1938, when he held titles at featherweight, welterweight, and lightweight. He first won the world featherweight championship by stopping Petey Sarron in six rounds in 1937. He then defeated Barney Ross for the welterweight title and Lou Ambers for the lightweight championship.

The achievement required Armstrong to compete across divisions with very different weight limits. He eventually vacated the featherweight title because maintaining the 126-pound limit was no longer practical. That detail matters: he held all three championships at the same time, but he did not keep them indefinitely.

Armstrong is also regarded as one of boxing's greatest pressure fighters. In 1937 and 1938, he recorded a remarkable streak of 27 consecutive knockout victories. Modern boxing trivia sometimes mixes up simultaneous championships with becoming champion in three divisions at different points. Those are separate accomplishments, and Armstrong's distinction specifically concerns holding three world titles concurrently.