I can pretend like I know all of this, but i can also be honest and say i stole this list from this website:
http://www.geocities.com/Baja/9660/linear.html
1.John L. Sullivan, the Boston Strong Boy (1885-1892)
2.James J. Corbett, Gentleman Jim (1892-1897)
3.Bob Fitzsimmons, Ruby Robert (1897-1899)
4.James J. Jeffries, the Boilermaker (1899-1905, retired undefeated)
5.Marvin Hart (1905-1906)
6.Tommy Burns, (1906-1908)
7.Jack Johnson, "Lil' Athtur" 1908-1915
8.Jess Willard, the Pottawatomie Giant (1915-1919)
9.Jack Dempsey, the Manassa Mauler (1919-1926)
10.Gene Tunney, the Fighting Marine (1926 -- retired July 31, 1928)
11.Max Schmeling, the Black Uhlan (1930-1932)
12.Jack Sharkey, the Boston Gob 1932-1933
13.Primo Carnera, the Ambling Alp 1933-1934
14.Max Baer, The "Livermore Larruper"(1934-1935)
15.James J. Braddock, the Cinderella Man (1935-1937)
16.Joe Louis, the Brown Bomber (1937-1949, retires)
17.Ezzard Charles, the Cincinnatti Flash (1949-1951)
18."Jersey" Joe Walcott 1951-1952
19.Rocky Marciano, the Brocton Blockbuster 1952-1956,retires, April 1956
20.Floyd Patterson 1956-1959
21.Ingemar Johansson 1959-1960
22.Floyd Patterson 1960-1962
23.Charles "Sonny" Liston 1962-1964
24.Cassius Clay, the Louisville Lip (aka Cassius X & Muhammad Ali) retires Feb. 1, 1970
25."Smokin" Joe Frazier 1970-1973
26.George Foreman, 1973-1974
27.Muhammad Ali, The Greatest 1974-1978
28.Leon Spinks 1978
29.Muhammad Ali (1978-1979, retires 9/79)
30.Larry Holmes(1980-1985)
31.Michael Spinks (1985-1988)
32."Iron" Mike Tyson (1988-1990)
33.James "Buster" Douglas (1990)