The Shaman caste is a group of charr that once spanned throughout all of the High Legions, particularly the Flame Legion. They are powerful magic users and were the main leaders of the legions. Now they are little more than outcasts in charr society, only allowed to remain because of their magical strength.
The Shaman caste was the ruling class of the charr around the time of the Searing. It was they who met in secret and decided to accept the titans as their new gods in exchange for the power to crush their hated foes, the humans. Gifted with the Cauldron of Cataclysm, they summoned gigantic crystal meteors to destroy the Great Northern Wall allowing them to assault the human kingdom of Ascalon.
Shortly after the widespread acceptance of the titans and Shamans and long before the Searing, Bathea Havocbringer stood in defiance against it, believing as all charr once did that there was no race stronger than the charr and that paying respects to any "gods" was heresy. For this, she was executed and offered as a sacrifice to the titans by the Shamans, who proceeded to remove female charr from the ranks of the legions and power.
A few years after the Searing, a collection of human champions destroyed the titans, leaving the charr disorganized for the moment. Struggling to maintain their hold on charr society, the Shamans soon rallied under a new set of gods: the Destroyers. Even at this time, discontent was brewing within the charr ranks, notably with the cunning Pyre Fierceshot. Together with a group of humans, he cast down the Shaman leader Hierophant Burntsoul and his new gods, telling all those present that there are no gods for the charr.
In time, more and more of the Shamans' powers were usurped, the final blow being dealt by Kalla Scorchrazor, granddaughter of Pyre Fierceshot. On the Plains of Golghein she and her forces overthrew the Flame Legion and its Shamans' hold on all the charr.