Old King Coal is the 3rd boss in the video game; Banjo-Tooie. He's also known as; the Grubby Boiler Monarch. He owns, controls, and lives in the train that can transport Banjo and Kazooie to any train station, named Chuffy. Old King Coal is a giant monster made entirely out of coal.
After Mumbo Jumbo uses his magic to lift Chuffy, Banjo and Kazooie explore the train. A voice warned them not to go inside the boiler, but they go inside anyway. When they enter the boiler, the door behind them is sealed shut, and Old King Coal shows his face and fights the bear and bird. All the eggs except for the Fire Eggs can deal damage to Old King Coal, with the Grenade Eggs and Ice Eggs dealing the most damage. Old King Coal will use a ramming attack and start turning up the heat every few seconds. The heat will suffocate Banjo and Kazooie, and if they touch the red areas they inflict damage on themselves. If Banjo and Kazooie stand on the black debris, Old King Coal cannot harm them. If Banjo and Kazooie can't defeat Old King Coal within a certain time limit the heat with be turn on forever, and they have a short period of time before they sufforcate to death. When Old King Coal is dealt a certain ammount of damage, a body part falls off, first his right arm, then his left, then his top half and finally his lower half. After Banjo and Kazooie defeat him, Old King Coal gives them permission to use Chuffy anytime they want.
Before the boss battle, Kazooie ask if Old King Coal if he's supposed to have a merry old soul, since his name is a parody to Old King Cole.
Not including the Klungo boss battles, and the Hag 1/Gruntilda boss battle, Old King Coal is the only boss in Banjo-Tooie that must be defeated in order to complete the game, because in one of the levels; Grunty Industries, Banjo and Kazooie need to use Chuffy in order to enter the building. But in order to use Chuffy, they have to defeat Old King Coal.
Despite him appearing to be menacing, Old King Coal is actually pathetically weak, and is consider by many to be one of the weakest bosses in video game history. This may be justified, as the player would need to use his train in order to enter places like Grunty Industries, and the game would be considered "unwinnable" if he was tough.