One of the original finders of the Souls of Lords, Gwyn ascended to become the Lord of Sunlight, and later Cinder. He fought alongside the other Lords to defeat the dragons and begin the Age of Fire, and ruled over Lodran with his children, also deities, Gwynevere and Gwyndolin, as well as a large number of other Gods.
As time went by, the Flame, and with it the Lords' power, began to fade. In an attempt to prevent the collapse of all life, and preserve the Age of Fire, Gwyn led his army of Black Knights to the Kiln of the First Flame and attempted to link the fire. He was unsuccessful, however, possibly due to him having gave his Lord Soul, and with it much of his power, to his confidant Seath the Scaleless and the Four Kings of New Londo. His mission failed, and with so little left of himself, Gwyn became Hollow while the rest of Lordan grew dimmer.
Under his command is an army of trustworthy knights, the black knights who stalk Lordran. There were also four higher ranking knights, Ornstein, Ciaran, Artorias and Gough. He once led the Silver Knights as well, when he was the Lord of Sunlight, however his loss of Godly Status had cost him his grip across the outside world after lighting the Flame for the second time.
One of the original Lords, Gwyn was quite easily a deity figure. His power was easily greater than that of the other Lords, and because of that he was the one to rule. In the beginning, Gwyn used his Sunlight Spears to shear away the stone Scales of Immortality of the dragons so that his knights and the other Lords could kill them. Much later, even after having given up much of his power, Gwyn was still a formidable force, wielding nothing more than his trusted greatsword.