He has black teeth, wears rusty plate armour, its helm displaying a crouching toad-dragon and whose filthy tabard bears the symbol of the Order. Carkus bears a sword that was ancient when the Blighted Duchies were still young. 
When his father died, he had not yet become a knight and so was not able to inherit the duchy. Instead a tourney ws held to find a new duke, which he demanded to enter and was granted permission by the Lady of Cankerwall herself. 
|My lady. I will save you, though I must brave the crystal labyrinths of the Great Foe himself. Though I must wade through seas of blood and traverse glades of silk, your truest kinght shall bring you home to the garden once more
~ Carkus Gryme.