The rat king wasn't actually the king of the rats.
He was one of the possible heirs to the crown because of his many accomplishments and contribution to the advances of the rat kingdom but the current king then favoured another rat called ratrising thus crowning him instead of the rat king.
Angered because he had always believed that he would be the king, he started a rebellion against the ratrising.
He failed and would have almost been executed had it not been intervention by the goblin king who was the dictator of all evil things in the land.The goblin king decided that he liked the rat king's courage and ruthlessness(he slain his own brother in an attempt to kill the ratrising) and decided to give him a position in the goblin king's lair as the gk had an unused sewers level.
The barbed choker was a gift from the goblin king to enhance his combat prowess and the goblin king sent a detachment of his men to serve the ratking and also allowed those ratlings that had survived the rebellion by letting them stay with the rat king.
The rat king was extremely thankful to the goblin king for sparing his life and swore his life to him.
the end
