The Platinum Legion were an organisation of followers of Bahamut operating from some time in prehistory (around 5000BNE) until the First Cataclysm (around 2000BNE).
They believed themselves to be the arbiters of justice and order, and with Bahamut's help they spread their brand of order around the world. They were generally well regarded and welcomed in civilised society, although some criticised their black and white view of the world and their policy of putting evil to death without much consideration for nuance.
The man who would be leader of the Legion travels with the Lords of Goon's folly, but he lacks the faith in Bahamut to spread his brand of justice.