I have to tell you that the things you've read (presumably on Wikipedia) about "Black Caesar" with the story about him being an escaped slave and such are all a modern invention. Almost none of that is supported by any contemporary sources. This is a very good essay by Devin Leigh that traces a lot of these misconceptions surrounding the myth of Black Caesar.

However, although the reality is murky, there are some underlying facts: a black man named Caesar was a member of Edward Thache (Blackbeard)'s crew. I've written a 9 part post about pirates and race here (that shows how pirates were in fact not remotely egalitarian or opposed to slavery) and in part 5 I discuss "Black Caesar." I'll copy from that here and expand on it a little.

It is true that of the 18 men Edward Thache had with him during his final engagement on November 22, 1718, 6 of them were black, and one of them was called Caesar. However, Thache himself repeatedly demonstrated that he was not opposed to slavery as he would routinely sell the slaves he captured for profit. His famous flagship, Queen Anne's Revenge, had formerly been a large French slave ship called La Concorda that he captured in the Caribbean in 1717 before selling the human cargo at Martinique. In April 1718, after capturing a ship carrying slaves in North Carolina, Thache casually remarked concerning the 14 "negores" he took out that he had gotten himself a "baker's dozen":

That the said Bonnet and Crew took out of the Pink they met as they came from Topsail-Inlet an Anchor and Cable; and that said Thatch took out of the Brigantine he took off the Bar of Charles-town fourteen Negroes; and that he heard Thatch tell the Commander of the said Brigantine, That he had got a Baker's Dozen. (from the deposition of Ignatius Pell who was a member of Stede Bonnet's crew, taken from Pirates in Their Own Words by E.T. Fox, p. 106)

All of the 6 black men that appear to have been members of Blackbeard's crew were executed for piracy but none of them were allowed to testify in their own defense at trial. This suggests two things: one that they were actually active members of the pirate crew (as the 70 slaves captured with Bartholomew Roberts in 1722 who appear to have been treated purely as slaves by the pirates were merely sold back into slavery while the white pirates were hung) but secondly that they may have nonetheless been legally still slaves, as slaves were not allowed to testify in court. Further evidence that the 6 blacks aboard Thache's ship during his final engagement were active and ostensibly willing members of the crew comes from two accounts based on the testimony of prisoners who were held on Blackbeard's ship at the time of the engagement. One is recorded in Charles Johnson’s A General History of the Robberies and Murders of the Most Notorious Pyrates published 1724:

Teach had little or no Hopes of escaping, and therefore had posted a resolute Fellow, a Negro, whom he had bred up, with a lighted match, in the Powder-Room, with Commands to blow up, when he should give him Orders, which was as soon as the Lieutenant and his Men could have entered, that so he might have destroy’d his Conquerors; and then when the Negro found how it went with Black-beard, he could hardly be persuaded from the rash Action, by two Prisoners that were then in the Hold of the Sloop. (A General History, 85)

The above account is corroborated by the unpublished personal letters of Governor Alexander Spotswood who gives the same account:

His orders were to blow up his own vessell if he should happen to be overcome, and a negro was ready to set fire to the powder, had he not been luckily prevented by a planter forced on board the night before and who lay in the hold of the sloop during the action of the pyrats. Tach with nine of his crew were killed, and three white men and six negros were taken alive but all much wounded. (Calendar of State Papers for America and the West Indies: December 1718)

Nowhere in either of these two accounts is it specified that the negro who was set by Blackbeard to blow up the powder room was the one named Caesar as opposed to any one of the other five blacks onboard, but whether it was him or another isn’t very important. The bit about Thache having “bred up” the negro (in addition to the fact that his testimony was ruled inadmissible at his own trial) further suggests that either this man was a slave or had recently been a slave owned by Thache, although his apparent loyalty to Thache and the fact that Thache trusted him maybe suggests he had been a slave but Thache had either unofficially freed him or promised to free him as the buccaneer Bartholomew Sharp had done in the 1680s with a loyal negro who died fighting at Arica (as I discussed here). Either way, this wouldn't make Edward Thache some kind of egalitarian considering his barbaric treatment of hundreds of other African slaves who fell into his hands who he simply sold as human cargo. Rather, Thache was a typical pirate who was primarily motivated by opportunistic greed.

Again, I invite people who are interested in more information about pirates and race to check out the 9 part post I made about this. I'll end with a quote from the pirate historian Benerson Little:

Golden Age pirates functioned as democracies, yet they chose to engage in the slave trade and treat most members of several peoples as worthy of nothing more than slavery. Only the few free blacks, mulattos, mestizos, zambos (mixed African and Native American), and Native Americans whom pirates permitted into their crews were granted the same rights and respect they accorded themselves. The rest they regarded as property, whether free or already enslaved.

…

The myth of Golden Age pirates as colorblind is fairly recent and has two origins. First, many scholars have promoted pirates of color to their rightful place in history. However, in doing this, they have often sought to diminish the role of the pirate as slaver, in order to improve the pirate’s image—less racist and more egalitarian, in other words. Second, Hollywood and popular fiction have also had a strong role, primarily by ignoring slavery as a critical aspect of piracy.

…

Authors and screenwriters have long realized that accurate depictions of how pirates treated slaves might put off much of the audience. The pirate as slaver does not fit the modern myth of the pirate as a social and political rebel—as a colorblind Robin Hood, so to speak. Even when Hollywood depicts pirates freeing oppressed populations (something pirates never really did), the populations are usually white. The Hollywood and video game ideals, seen for example in Rage of the Buccaneers and “Assassin’s Creed Freedom Cry,” of pirates freeing slaves out of a sense of moral obligation derived from anti-slavery beliefs, has no basis in fact, no matter how appealing these ideals are. (The Golden Age of Piracy: The truth behind the myths by Benerson Little, 200, 206-7)