King Quallus was the owner of the legendary Quallus Collection of which the Kronos Stone was a part; Until, that is, Autolycus stole it. Quallus had nicknamed the stone "The Quallus Crystal" (HTLJ "The End of the Beginning.")
In an alternate timeline created by Callisto and Hope, Quallus offered the Kronos Stone to Xena in hopes that she would spare his kingdom. Instead, she took the offering and had Quallus killed. She sent his body back to his people and kept his head as a trophy (HTLJ "Armageddon Now Part 2").