In 1919, when he was 37 years old, he lost the title in an extremely one-sided loss by declining to come out for the fourth round against Jack Dempsey, who became a more celebrated champion.

[5] The matter has never been resolved, with contemporaneous ringside sports journalist reporting in The New York Times that Willard spat out at least one tooth and was "a fountain of blood" increasingly discounted in favor of a view that he had only a cut lip and a little bruising.

[6] A powerfully built 6 ft 6+1⁄2 in (1.99 m) and 245 lb (111 kg), Willard did not begin boxing until the age of 27, but proved successful, defeating top-ranked opponents to earn a chance to fight for the Championship.

He was a gentle and friendly person and did not enjoy boxing or hurting people, so often waited until his opponent attacked him before punching back, which made him feel at ease as if he were defending himself.

He was often maligned as an uncoordinated oaf rather than a skilled boxer, but his counter-punching style, coupled with his enormous strength and stamina, proved successful against top fighters.

On April 5, 1915, in front of a huge crowd at the new Oriental Park Racetrack in Havana, Cuba, he knocked out champion Jack Johnson in the 26th round to win the world heavyweight boxing championship.

Willard fought several times over the next four years, but made only one official title defense prior to 1919, defeating Frank Moran on March 25, 1916, at Madison Square Garden.

At one point Dempsey left the ring mistakenly thinking the fight was over, and under the rules could have been disqualified, but Willard had economised by not employing professional cornermen and they failed to insist on application of the regulations.

Tyson, a great admirer of Dempsey's, admitted that "he just did whatever Jack Kearns told him to do" and "in those days anything could have happened", for that there was no agency or other legal authority at the time that was officially empowered to oversee and protect fighters from violations of such kind.

However, footage before the fight shows Dempsey putting on his gloves with no additional objects and in full view of Willard, his team and the crowd.

[3] On May 12, 1923, promoter Tex Rickard arranged for Willard to make a comeback, fighting Floyd Johnson as part of the first line-up of boxing matches at the newly opened Yankee Stadium in New York City.

[4] Willard and a dispute he had with Harry Houdini is the topic of Andy Duncan's Nebula Award nominated novella The Pottawatomie Giant.

[16] In 2020, a television program Antiques Roadshow – Crocker Art Museum (Season 24, Episode 8, Part 2), showed a photograph from his 5 April 1915 championship winning match, and the commemorative pocket watch Willard carried which was valued at between $15,000 and $50,000.