Kuma is a character that is key to the current events of One Piece. The Egghead Island arc is heavily centered around him and his importance to the overarching plot and, with each passing chapter, Oda has been revealing bits about him through either his daughter, Jewelry Bonney, or through him directly. While Kuma has been involved in a big chunk of the ongoing arc, his life still remains to be a big mystery to the fans.
There is very little that Oda has made known about Kuma and whatever fans know is also very obscure at this point in time. That said, there are several hints that have been sprinkled over the Egghead Island arc so far that tell fans quite a lot about the tragic life that Kuma has led. On top of that, the previous chapter of One Piece, One Piece 1074, gave fans a brief flashback of Kuma as a child. While much of it was silhouetted, fans could make out quite a great deal about his past which was full of nothing but pain and misery.
Kuma As A Slave
As seen in the flashback that fans got in the previous chapter of One Piece, Bartholomew Kuma was subjected to incredible pain as a mere child. In the flashback, fans saw Kuma being beaten by the people of his hometown and being forced to return to power with significant power. While silhouetted, it is quite clear that those who wanted him were none other than the Celestial Dragons. This is very similar to the case of Boa Hancock, another Warlord of the Sea, who was sold by humans to the Celestial Dragons and enslaved until she was eventually freed by none other than Fisher Tiger.
Bartholomew Kuma was beaten bloody as a kid and forcefully turned over to the Celestial Dragons. What is interesting to note here is, however, the fact that Kuma said he didn't want to go back to that place. This implies that Kuma was, in fact, already a slave at this point and was branded by the hoof of the dragon too. He then got away somehow, however, the Celestial Dragons came back for him and took him prisoner once again. Kuma is known to have escaped later on, as was seen in the flashback with Vegapunk, however, the fact that he was known as the pawn of the Celestial Dragons is enough proof that he sold himself back to them, for some reason.
Why Kuma Was Enslaved
Kuma was certainly enslaved for a particular reason that was, by the looks of it, interesting to the World Government. While it is true that the World Government enslave anyone they see fit and don't need a reason to put a person in chains, with Kuma, things are more than just that. This is clear from the fact that the World Government threatened to kill everyone in Kuma's hometown if he wasn't turned over to them immediately. This ended up becoming the reason why his own people turned on him, beat him and, eventually, sold him to the Celestial Dragons. Not so long ago, Oda brought forward the idea that Bartholomew Kuma was, in fact, a member of a special race of people.
What exactly this race is remains a mystery for now, however, it is most certainly the reason why Kuma was hunted by the Celestial Dragons. It could be that being of this race made Kuma a more exotic slave to them, or, perhaps, the very existence of Bartholomew Kuma could've spelled danger for them and thus, they enslaved him – branding him with the hoof of the dragon. The secrets of Kuma's race aren't known to fans just yet, however, as the Egghead Island arc continues, all of them will be unraveled. More likely than not, Kuma's race will be linked to the Ancient Kingdom of the past and thus his erasure would've meant a symbolic victory of sorts for the World Government.
Why Kuma Agreed To Become A Slave Again
It is a known fact that Kuma escaped from slavery time and again. After all, the very beginning of his flashback introduced him to the fans as a runaway slave despite being a child. Kuma was eventually given back to the Nobles to torture and abuse and, thus, he came to be known as the pawn of the Celestial Dragons. Yet, Kuma could very well have escaped. Fans know for a fact that he ended up becoming the King of Sorbet Kingdom and not just that, but he also became a vicious pirate. He was also one of the founding members of the Revolutionary Army and this is indication enough that Kuma was, in fact, in a position to have escaped his captors.
Yet, for some reason, he chose to become their lapdog and even volunteer for the Pacifista Project. The reasons for this could be multifaceted. For one, fans know that Vegapunk is linked to Dragon and is his ally. The two are trying to turn the world upside down together and bring down the World Nobles and those in power. As such, Kuma was, in one way, in the safe hands of Vegapunk. However, the main reason for him to give himself up voluntarily to the Nobles could simply be for Bonney's protection. If Bonney shares blood with Kuma, it is possible that she could've faced the same fate as him. In fact, fans know already that she was hunted by the Celestial Dragons as well and escaped from their grasp several times. Kuma most likely gave himself up so the Government out of him what they would otherwise attempt to get from Bonney.