Louis, Ali and Jack Johnson in any order you want are the correct answers here. IMO the top 3 are pretty obvious. The gap comes after 3.
1. Ali 2. Louis 3. Tyson These are the fighters that people remember. Also they made boxing famous globally.
1. Lennox Lewis 2. wlad klitschko 3. George Foreman 4. Holyfield 5. Tyson 6. Holmes 7. Vitali 8. Ali 9. liston 10. marciano
There I corrected it for you. You do know that Ali knocked Foreman out in the 8th round in South Africa don't you? And Tyson and Holyfield don't belong in even the top 20. But that's arguable, I guess.