Johnson became the first African-American to win boxing's heavyweight crown Dec. 26, 1908, a century before Obama's election as the nation's first black president and nearly 40 years before Jackie Robinson broke the color barrier in Major League Baseball.
Johnson's record in the ring against his mostly white opponents spurred the furious search for a "Great White Hope."
For years, Johnson sought a fight with James Jeffries, a hulking white boxer who reigned as heavyweight champion for nearly six years.
Jeffries left the sport rather than face Johnson and risk losing. But, later, he was persuaded to leave retirement and step into the ring for the ultimate showdown.
The Johnson-Jeffries fight July 4, 1910, in Reno, Nev., was deemed the "Battle of the Century," two titans of the sport fighting with not just a title on the line but significant racial issues as well.
"I am going into this fight for the sole purpose of proving that a white man is better than a Negro," Jeffries said before the fight.
But Johnson prevailed over Jeffries in the 15-round fight. His victory sparked deadly race riots and violence across the nation and further fueled the hostility directed at Johnson.
In 1910, Congress passed the Mann Act, which made it unlawful to transport women across state lines "for the purpose of prostitution, debauchery, or for any other immoral purpose."
The bill was aimed at cracking down on prostitution but some people believe it was used against Johnson as retribution for his success in the ring and his lifestyle.
Law enforcement authorities first targeted Johnson's relationship with a white woman named Lucille Cameron. But the two got married and she refused to cooperate with the investigation.
Another former lover of Johnson's, a white woman named Belle Schreiber, came forward to testify against him.
Based on her testimony, Johnson was convicted in 1913 of violating the Mann Act. He fled to France before he was sentenced in order to avoid punishment.
Johnson's story was chronicled in Ken Burns' 2005 documentary, "Unforgivable Blackness: The Rise and Fall of Jack Johnson."
The prosecutor in the case said after the verdict that Johnson was made into a scapegoat, according to the documentary.
"This Negro, in the eyes of many, has been persecuted," the prosecutor said. "Perhaps as an individual he was. But it was his misfortune to be the foremost example of the evil in permitting the intermarriage of whites and blacks."
His reign as heavyweight champion came to an end when he lost to a white boxer, Jess Willard, in a fight in Cuba in 1915. He returned to the United States in 1920 to surrender to authorities and served 10 months in prison.
Johnson tried to resuscitate his boxing career but he never regained his crown. The former champion died in a car accident in North Carolina in 1946 at the age of 68.
In April, McCain and King appeared with three of Johnson's relatives to announce their resolution urging a presidential pardon.
"We need to erase this act of racism which sent an American citizen to prison on a trumped-up charge," McCain said then. "I have great confidence this president will be more than eager to sign this legislation and pardon Jack Johnson."