Jack Johnson's story is remarkable.
Interesting tidbits: Johnson, who grew up in Galveston, Texas (USA) -- residing literally a city block or so from where I was reared -- was a product of an environment that was very much unlike most of the southern USA at that time. During the late 1880s of Johnson's upbringing, Galveston was a booming port city on the Gulf of Mexico, and was a location where many African-Americans converged to find viable means to make a living that were unavailable elsewhere in that region. Additionally, the local African-American community then was also populated with a substantial number of professionally-trained educators who had already descended to Galveston during the Reconstruction era that followed the Civil War. Recall that Galveston was also the seaport through which Civil War-era President Abraham Lincoln's Emancipation Proclamation was first introduced and enforced in the former Confederacy.
This all had a large role to play in Jack Johnson's social outlook and intellectual foundation. For more information regarding Jack Johnson, I recommend the book,
Island of Color: Where Juneteenth Started, written by Izola Fedford Collins (my mother).
Island of Color also provides insight regarding Jack Johnson's somewhat controversial social choices, explaining that his childhood's racial climate was far less polarized than was most of the Old South. Galveston's public accommodations were not functionally segregated until Texas later adopted so-called "Jim Crow" laws that other southern USA states enacted expressly to nullify Reconstruction era reforms.