Well as a laymen & not a historian.
I know it may be hard for some today to believe(considering Black prominece in todays sports) but Black Americans were generally considered physically inferior to Whites at the turn of the 20th cenury. It was thought that Blacks could not physically nor mentally stand toe to toe with a White man in a boxing Ring. :dunno:
Jack Johson smashed this myth of Black inferiority when he became the 1st Black Heavyweight Champ & completely destroyed a revolving door of "Great White Hopes"(as they were called) for seven(7) straight years between 1908-1915.
He did this during a time when Blacks could be lynched for saying the wrong thing to a White person(especially in the South),daring to look at a White woman,etc....Yet Johnson would taunt his White opponents in the Ring,taunt the media ringside who despised him , taunt the White fans who came to see him lose & then leave the fight with one of his many White wives/girlfriends. He was White America's worst nightmare personified.
He was Muhammed Ali 50 years before Ali. Johson was extremely flamboyant ,garish stlye(gold teeth ,fancy cars/clothes/women/clubs)predicted the round he would knock out his opponent,confident & basically drove a disgusted White America nuts for 7 years. (Even set off race riots in 1909 which killed early 30 people when he beat Jack Jeffries)
He was so despised by Whites(& equally adored by most Blacks) that another Black would not get a shot at the title for over twenty years(Joe Louis who was much more humble & accepted by Whites) ,but Johnson had already defeated the myths about Black Athletes decades before Joe Louis.
I would recommend getting a dvd copy of the Johnson biography: "UNFORGIVEABLE BLACKNESS" by Ken Burns.( I found a used one at Amazon for $9). A book by the same name also by Jeffry(?) Ward .
http://www.youtube.com/watch?v=VLE5JxGwIuk