stereotypical name for male black person (now only derogatory), 1818, American English, probably a different word from sambo (n.1); like many such words (Cuffy, Rastus, etc.) a common personal name among U.S. blacks in the slavery days (first attested 1704 in Boston), probably from an African source, such as Foulah sambo "uncle," or a similar Hausa word meaning "second son."
It could be used without conscious racism or contempt until circa World War II. When the word fell from polite usage, collateral casualties included the enormously popular children's book "The Story of Little Black Sambo" (by Helen Bannerman), which is about an East Indian child, and the Sambo's Restaurant chain, a U.S. pancake-specialty joint originally opened in Santa Barbara, Calif., in 1957 (the name supposedly from a merging of the names of the founders, Sam Battistone and Newell "Bo" Bohnett, but the chain's decor and advertising leaned heavily on the book), which once counted 1,200 units coast-to-coast. Civil rights agitation against it began in 1970s and the chain collapsed, though the original restaurant still is open. Many of the defunct restaurants were taken over by rival Denny's.