So a lot of you might be wondering who the hell is this dead uncle and why is he after Jax. Now, I can't tell you why is he's after Jax but I could tell you who is this "uncle".If you go back and read His Baby one, chapter chapter 37, it talks about the "dead uncle".
[if you're a lazy piece of shit like me who doesn't feel like re-reading and what not, then here's a screenshot]