I was also going to go more literal. George Washington was the first president, so I gotta go with the first HW Champ John L Sullivan. Thomas Jefferson was the quintessential Virginian, so we could have fellow Virginia man Pernell Whitaker. Teddy Roosevelt charged up San Juan Hill, so perhaps a Puerto Rican great like Wilfredo Gomez. Abraham Lincoln issued the Emancipation Proclamation and was a controversial figure so he would be represented by Muhammad Ali. Edit: the San Juan Hill in question was actually in Cuba, so replace Gomez with Kid Gavilan.
John L, Joe Louis, Robinson, Ali John L was the first Joe Louis the longest reigning SRR considered the best to do it Ali for being first 3 time champ, his courage in the ring and an activist inside and outside the ring.