Kezeroth is an incredibly powerful entity who is feared for being known as the "World Ender". He plans to live up to his name by freeing the ancient beast Quetzal from its prison in a frozen comet passing by Lore every 26,000 years. His first attempt to do so failed at the hands of the legendary hero Elim, who redirected the beam of energy that would've brought Quetzal itself down to Lore to end it away from it, so the ChronoCorruptors froze him in time for another 26,000 years so they could take the liberty of fixing the temple for him and give him another chance to free the beast Quetzal. Athon, a Chronomancer who was watching Elim stop Kezeroth's plans, saw the ChronoCorruptors do their job, and went to the players for help in defeating Kezeroth again and preventing the end of all things.
The ChronoCorruptors unsealed Kezeroth anyway and he was then able to free Quetzal from its prison. Luckily, the players and Athon retrieved the Sword of Hope from the bottom of the FrostDeep Dungeon below the temple and teleported out before the comet hit the temple. After the players defeated Quetzal, Kezeroth, having seen the outcome of the battle, angrily finished off Quetzal himself as punishment for failing to bring about the end of all things before breaking the sword, and he departed for Ice Rise Keep telling the players to stay out of his way.
The players decided not to heed his words anyway and they stormed the keep to confront Kezeroth. As the players dealt as much damage to him as possible, it became apparent that Kezeroth was proving to be unstoppable until Athon got an idea. The Chronomancer gave his life to save Lore from Kezeroth by using up all of his energy to freeze Kezeroth in time for another 26,000 years or even longer.