On July 4, 1910, a black heavyweight champion battered and knocked out a white challenger in 15 one-sided rounds. For the past 95 years, White America has been trying to win that fight back.

No sporting event in American history has had the impact that fight between Jack Johnson, the first black man to wear the heavyweight crown, and Jim Jeffries, his predecessor, had and continues to have on not only a sport, but the country.

Tonight at 9 p.m., on the occasion of what would have been the Reverend Martin Luther King’s 76th birthday, PBS airs a four-hour, two-part documentary called “Unforgivable Blackness: The Rise and Fall of Jack Johnson” directed by Ken Burns and based on the book by Geoffrey C. Ward.

The program will explore a forgotten fight and a largely forgotten champion, both of whose effects are still being felt.

Johnson, the first black man ever allowed to compete for a prize that was long considered the exclusive property of the white man, was the forerunner of the modern athlete – proud, showy, boastful, and unashamedly black. He described himself, aptly, as “The brunette in a blond town,” and had no intention of bleaching his hair, his skin color, or his way of life.

In many ways, Jack Johnson was the white man’s worst nightmare, the black man who refused to know or accept “his place” in White America. Johnson would fight for the white man’s title and beat the white man’s champion. Worst of all, he would marry the white man’s women. This last was truly the unforgivable sin, the one for which Johnson was forced into exile while still a champion and eventually railroaded into prison for violating of the Mann Act, an archaic law originally written for the prosecution of pimps and prostitutes.

Jeffries was a giant for his time, a brawler who had never lost nor been knocked off his feet when he retired unbeaten in 1905 and was allowed to anoint his own successor. To many Americans, he was the ideal man – big, strong, fearless, quiet, and best of all, white.

After Johnson knocked out Canada’s Tommy Burns to win the title in 1908, the cry arose for Jeffries to end his retirement and “rescue” the white race. Johnson, who had put in years of lobbying, begging and pleading for a chance, proceeded to mow down white challenger after white challenger, and Jeffries reluctantly agreed to fight him.

The entire country, it seemed, was rooting hard against Johnson in 1910. Some of boxing’s most famous names, John L. Sullivan and “Gentleman Jim” Corbett (a boyhood idol of Johnson’s) lined up behind the 37-year-old Jeffries, who had tortured 100 pounds off his indolent body in order to give the appearance of The Boilermaker of old.

But the fight was an ugly mismatch. As Johnson battered the helpless Jeffries, the champion directed a steady stream of wisecracks at Sullivan and Corbett, who were suffering at ringside. When Johnson finally ended it, leaving Jeffries in a bloodied and exhausted heap, police jumped into the ring to prevent a riot. Films of the fight, which were expected to generate thousands in added revenue for both fighters, were impounded and not shown to the public for years.

Across the country, race riots broke out as news of Jeffries’s defeat spread, and at least 20 black Americans were murdered. It is no coincidence that after Johnson met defeat at the hands of Jess Willard in 1915 – that fight had to be held in Havana because Johnson could not return to the U.S. – no black man was allowed to fight for the title for more than 20 years. And that man, Joe Louis, was the public antithesis of Johnson and more like White America’s idea of an acceptable black man.

These days, it has become fashionable to characterize Louis’s second fight with Max Schmeling, a German and a favorite of Adolf Hitler in the 1930s, as the most important and influential sporting event of all time because of its implications for and parallels with the rise of the Nazi empire. But Louis-Schmeling was an aberration, the serendipitous meeting of the representatives of two nations about to go to war. Johnson-Jeffries was far more important, and more germane, because it epitomized race relations in 1910, and continues to do so nearly a century later.

Whether it is fair or not, Rocky Marciano, Gerry Cooney, Duane Bobick, Andrew Golota, and both Klitschkos are the direct descendants of Jim Jeffries, white boxers who carried more than their own hopes of wealth and glory into the ring against black opponents. With the exception of Marciano, each found himself qualified to fight for the heavyweight title for one reason above all others: the color of his skin.

And when the direct descendant of Jack Johnson, Muhammad Ali, was at the peak of his powers, White America turned to an “acceptable” black man, Joe Frazier, to carry the mantle normally reserved for a white boxer. Frazier became the “white man” sent in to save a divided nation from the threat of Ali, who was every bit as frightening to White America in the 1960s and ’70s as Johnson was in 1910.

I will never forget watching the Cooney-Holmes fight at a movie theater in Queens, and after Larry Holmes had knocked Cooney out, seeing a white man walk over to the only black man in the place and smack him in the back of the head. This was New York City, 1982, but it might just have well been Reno in 1910.

Jim Jeffries may have been the first Great White Hope, but he was hardly the last. Ninety-five years after his defeat by Jack Johnson, far too many of us still refuse to accept the outcome.

Mr. Matthews is the host of the “Wally and the Keeg” sports talk show heard Monday-Friday from 10 a.m.-1 p.m. on 1050 ESPN Radio.