From the Glossary of The Wheel of Time

A society holding strict ascetic beliefs, dedicated to the defeat of the Dark One and the destruction of all Darkfriends. Founded during the War of the Hundred Years by Lothair Mantelar to proselytize against increasing numbers of Darkfriends, they evolved during the war into a completely military organization, extremely rigid in their beliefs and completely certain that only they know the truth and the right. They hate Aes Sedai, considering them, and any who support or befriend them, Darkfriends. They are known disparagingly as "Whitecloaks"; their sign is a golden sunburst on a field of white.