Who does Cacambo represent in the real world of Voltaire?

In Voltaire’s Candide, the character Cacambo is Candide’s servant or valet. Cacambo travels with Candide through El Dorado in South America (where they become separated), later reenters the action in Venice, and then helps his master travel to Turkey. His status as Candide’s “servant,” however, is complicated, because he is later enslaved by Sultan Achmet. Near the story’s end, Candide pays “a ransom” to free Cacambo. In relation to Voltaire’s writings about blacks and Africans, Cacambo occupies an ambivalent space.
The character Cacambo serves as a foil to Candide. Practical and cunning, he stands in contrast to Candide’s naivete and optimism. One of the book’s most well-known lines is Candide’s answer to Cacambo’s question, “What is this optimism?”

“Alas!” said Candide, “it is the madness of maintaining that everything is right when it is wrong.”

In numerous places, it is Cacambo’s pragmatism that saves the two of them from dire endings, such as when they encounter cannibals who want to make a meal of them. As a loyal servant and frequent interpreter with useful skills, Cacambo is a positive figure. In his cunning, deceit, and manipulation, however, he also corresponds to stereotypes of non-white people that abound in the literature of the time.
Cacambo’s name and initial description in Chapter 14 indicate that he is a person of color.

Candide had brought such a valet with him from Cadiz, as one often meets with on the coasts of Spain and in the American colonies. He was a quarter Spaniard, born of a mongrel in Tucuman; he had been singing-boy, sacristan, sailor, monk, pedlar, soldier, and lackey. His name was Cacambo, and he loved his master, because his master was a very good man.

In Chapter 26, he is described as “a man whose complexion was as black as soot.”
It was long assumed that Voltaire made up the name, and that it has plays on words associated with elements of his identity. One question is whether the name is pronounced as “kakambo” or “kasambo.” “Caca” is the Spanish slang word for “feces,” so including that element could indicate baseness and low status. Another possible association is with “cacao” and the brown color of chocolate, or “cacahuate,” Spanish for peanut, a food then associated with Africans. If pronounced with the initial s sound, however, the name connotes “sambo” (or “zambo”), Spanish for a mixed-race person; in the eigteenth-century casta racial hierarchy system, sambo was the term for a person with one African and one Native American parent.
The questions of race and slavery are clearly associated with Cacambo’s character and aspects of Voltaire’s life and nonfiction writings. The optimism line is delivered following a speech by a mutilated “negro” slave they encounter, who denounces the barbarities of slavery. Voltaire wrote against slavery in his Essay on the Blacks and the Spirit of the Nations. However, he did not see people of African heritage as equal to Caucasians, in part because he believed they descended from different ancestors (polygenesis) and wrote that they were less intelligent.
Source: Kjørholt, Ingvild Hagen (2012). Cosmopolitans, slaves, and the global market in Voltaire's Candide, ou l'optimisme. Eighteenth-Century Fiction, 25 (1): 61-84.
https://muse.jhu.edu/article/485730/pdf