Green’s Dictionary of Slang

a Native American who is considered insufficiently nationalistic and overly subservient to the white man by other Native Americans; occas. of blacks.

1972		D. Claerbaut Black Jargon in White America 84: Tonto n. a black male who is untrue to his race.
1983		‘Heat Moon’ Blue Highways 293: ‘Who’s the creep in my room?’ ‘The jigaboo?’ ‘No, Tonto.’.