Jaynis Kobb is the leader of Jaynistown.
Hating each other since birth, Jaynis and his brother, Taylor, have never overtly fought one another; opting instead to employ poison, traps, and assassins to do the other in. This has only made them stronger and more clever as they try to outwit and overcome each attempt made by the other on their life.
In order to access the Trash Coast to get the next fragment of the Vault key, Patricia Tannis sends you to negotiate with Taylor Kobb. He then asks you to kill Jaynis in the mission Jaynistown: A Brother's Love.
Take care of all the henchmen first, he is easier fought alone. Then just focus attacks on him, incendiary weapons work well.
Upon being killed, Jaynis Kobb will drop his unique weapon, The Meat Grinder.
Jaynis' name is a reference to the Firefly character, Jayne Cobb, a gunman whose violent, amoral outlook in many ways disguises a compassionate, if somewhat reluctant, hero (positive traits not shared by the character named for him in Borderlands). In the seventh episode, "Jaynestown", the characters enter a mining town where the locals hail Jayne (who had tried to steal money from the local magistrate years before, and ended up accidentally dumping the cashbox on the locals) as a hero in the same vein as Robin Hood.