The King Rings are rings that were given to Brady and Boomer after they passed the King Challenge. The rubys inside the rings were forged from Mount Spew. If someone who isn't royalty wears the ring, the ring will be stuck on said person's finger (or toe) and they will be located to the nearest royal and said person will be tried for treason. If either king is unworthy of wielding the ring, then the rings will destroy both of them.
Brady and Boomer unlocked a chamber where they met the ghost of King Malakai. King Kalakai tried to take the rings from the kings. He managed to retrieve them and tried to use them to sink Kinkow into the sea, but the kings stopped him and turned him back into a fish. (The Evil King)
Brady left his ring behind when he moved back to Chicago. Boomer tried to give it to Boz after he proved himself worthy of the throne, but a bat took it to the Dark side where it was found by the leader of the Tarantula People and given to Mary Ann. She tossed it off a cliff and Boomer retrieved it and gave it to Boz. (The New King)
Boz was proven to be an unworthy king after he and Boomer tried to use them together and the rings destroyed the pool table and Boz's King Ring failed to work. (Mysteries of Kinkow)