He is a young African-American boy. At first, Sambo is not named, only appearing dragging a sack toward a river and lamenting that he has been tasked with drowning a cat. The cat escapes and fills the sack with bricks, and calls Sambo by name to encourage him to throw in the (now cat-less) sack into the water. The unnamed cat then proceeds to 'haunt' Sambo until his disguise is washed off, at which point Sambo does kill him with a shotgun, after which the cat's nine lives reappear to haunt him for real.
Sambo is regarded as an offensive stereotype, being drawn in obvious blackface, leading to his cartoon being included in the infamous Censored Eleven, the only Looney Tunes release or Chuck Jones film on the list. There is another cartoon on the list, a Merrie Melodies short with Bugs Bunny called "All This and Rabbit Stew" that contains a similar (unnamed) blackface character, though there is no evidence of these characters being the same.