The Mob Leader is part of the Saber Quest. You can find him on the Jean-Luc Island between Magma Village and Bobby Island. He is a level 120 boss, and spawns every minute. When you defeat him, you gain 3000 bounty, unless you are already at 2.5 million bounty. This is the max bounty you can get from normal bosses, the exception being the rip_indra raid boss, which gives 100,000 Bounty upon defeat. The Mob Leader is the best boss for people who need help with getting a higher bounty because of his respawn time which is about a minute
This boss is the 3rd most easy boss in the game so he is an easy boss to kill for bounty/honor.