Trump was animated as he boasted about King's endorsement. But bringing King to the convention to testify in favor of Trump would be an odd move. Despite King's successes in the world of boxing--he has promoted almost every major boxer in the last 50 years--he has a long checkered past, filled with allegations of fraud.

A short list of some of King's sketchier moments includes:

In 1982, Muhammad Ali sued King for allegedly cheating him out of $1.1 million he was owed for fighting Larry Holmes. (Ali dropped the lawsuit after King paid him $50,000.)

In 1984, Larry Holmes sued King for allegedly cheating him out of several million dollars. (Holmes settled for $100,000.)

In 1987, boxer Tim Witherspoon sued King for $25 million, claiming King was violating anti-trust and racketeering laws. (Witherspoon and King settled out of court for $1 million.)

Investigations by Sports Illustrated and PBS' Frontline linked Don King to mob figures, including John Gotti, and the Frontline feature alleged that King had bribed a judge in Cleveland in 1967 to help him beat a murder rap. (King was found guilty of second-degree murder for stomping an employee to death over a debt, but the charge was later reduced by the judge to non-negligent manslaughter, and King served nearly four years. He was pardoned by the governor of Ohio in 1983.)

King has had problems with another one of Trump's celebrity endorsers: Mike Tyson. During some of the most tumultuous years of Tyson's career, Trump "advised" the heavyweight champion, while King promoted his fights. In the end, Tyson sued King for $100 million, alleging King cheated him out of millions. The case was settled for $14 million.