Green’s Dictionary of Slang

backra n.

also bockra, buccra(h), buckra(h)
[black patois of Surinam bakra, master. This in turn was based on Efik (the language of the Calabar coast) mba, all + kara to encompass, to get round, to master (a subject); thus mbakara, makara, a white man, a European, with a parallel meaning of a demon, a powerful and superior being (cf. ofay n.). Note the popular (if erroneous) ety. back raw; the white man was known for his beatings]
(W.I./US black)

1. [late 18C+] (also baccararo, baccra, backearay, bakra, buckruh) a white man.

2. [late 18C+] (also bochro, bockro, buckera, bukkra) a master, a boss.

3. [1920s] (US black) one who, while black, moves in white society and sees themselves as the white man’s equal.

In phrases

black backra (n.)

[1950s+] (W.I.) a respected black man.

walking backra (n.) [lit. a ‘walking white man’, i.e. one who had no horse and was thus forced to walk, was considered of the lowest rank] [early 19C] (W.I.)

a poor white.