King of the Fire Festival is an achievement awarded for completing the quest A Thief's Reward, which is offered once a character has completed all four "Stealing <city>'s Flame" quests. Completing this achievement is an objective of the meta achievements and .
To qualify, Horde characters must complete all four of
Alliance characters must complete all four of
In each case, a city's flame is stolen by clicking on the (aqua/blue tinted flames) of a city's fire. A quest starting item will appear in the character's inventory that offers the appropriate quest.