Yeh, nothing is known about him, except he is of course the former Captain of a merman pirate crew, which Arlong was apart of before they disbanded, when Jinbei became a Shichibukai pirate.
Perhaps he convinced the government to pardon Arlong & allowed his followers to leave the Grand line. Also the name Jinbei or 'Jinbeizame' translates into Whale Shark, so if he bears any resemblance to a Whale Shark, well… um, just think about it like this. If Tom's the merman equivalent of a Golden puffer, then Jinbei must be absolutely freakin' massive.
_(Believe me, I've actually dived with these magnificent creatures, two years ago off Ningaloo. They are the biggest known fish on the planet, very slow & graceful & not remotely aggressive.
So I'm intrigued to see how Oda will create this character)_