Thaddeus Spencer Jr. (March 28, 1943 – December 13, 2013) was an American heavyweight boxer.
A native of Portland, Oregon, Spencer made his professional boxing debut in May 1960.
With wins over contenders Doug Jones, Brian London, George Johnson, Tom McNeeley and Amos Lincoln, he was regarded highly enough to be a part of the eight-man WBA elimination tournament, held after Muhammad Ali had been stripped of the title.
Spencer won a 12-round decision over former title-holder Ernie Terrell in August 1967 and was then matched against Jerry Quarry in the semi-finals.
Spencer lost his next three fights by knockout, to Leotis Martin, Billy Walker and Mac Foster, and was never a serious title contender again.