He's the one and only streetlord in the town that the beasts occupy. He has three gangs under his control, and it's a rule by fear. The gangs together have no full name but the separate ones are the Raiders, the West, and Depth - Joker's original gang. Joker has a deep hatred for Blitz though he secretly fears that Blitz could become a streetlord himself and challenge Joker's rule.
In this background Joker is in the same place as Ryder. He is here at the same time as Flare, when the fog covers the lands.