The Nameless King

The Nameless King, also known as the King of the Storm, is an optional boss in Dark Souls III.

Description
A giant golden-armored man with long strands of bristling ash for hair, who wields a massive spear and rides atop a huge corvine dragon.

Location
Found in Archdragon Peak by ringing the bell located just before the Great Belfry bonfire.

Lore
The Nameless King was a dragon-slaying god of war in the Age of the Gods and heir to lightning, until he sacrificed everything to ally with the ancient dragons. He tamed a Stormdrake and formed a close bond with it, leading it to countless battles.

Dragonslayer Ornstein, another relic of the Age of Gods, left the ruined cathedral of ancient Anor Londo he once guarded in search of the Nameless King.

* It is heavily implied that the Nameless King is the long-speculated firstborn child of Gwyn, Lord of Sunlight. Long ago, the Nameless King was a god of war and heir to lightning. The firstborn was a god of war, and inherited sunlight, which manifests as lightning. The Nameless King wielded the Dragonslayer Swordspear, a weapon from the Age of Gods. The firstborn similarly wielded a great spear. The firstborn eventually committed a grave error, which led to the rescinding of his deific status and his removal from the annals of history, his name forgotten. The Nameless King sacrificed everything to ally with the ancient dragons, whom he once fought.

Given how the firstborn only had respect for arms, it's possible that he chose to ally with the dragons, believing them to be strong or perhaps because he disagreed with Gwyn's methods; hence why Gwyn would expunge him from history. However, it is unknown if the Nameless King allied with the dragons only after his expulsion or was ostracized because of it. However, it is known that the firstborn left the Sunlight Blade upon Gwyn's honorary coffin in Anor Londo, perhaps as a final farewell, which could only mean that Gwyn had already departed for the Kiln of the First Flame. Either the firstborn wasn't immediately expelled or returned to pay final respects, implying some remaining sentiment.

* ''Note: This section relies heavily on speculation. Very few facts are offered in game to substantiate most of the information here.''

Warrior of Sunlight
In Dark Souls, the Nameless King shares an iconic symbol with the Warrior of Sunlight covenant: the Sunlight Medal. The covenant itself is closely related to the firstborn, the members being referred to as his warriors, and the god is said to watch over the covenant closely.

Statues
In Dark Souls, a statue of a mother holding a sword-wielding child, thought to represent the Nameless King, is located in front the Sunlight Altar bonfire. This statue also appears in several places, such as above the Firelink Altar and behind the coffin holding the Darkmoon Seance Ring. The sword the child is wielding shares a distinct resemblance to the Sunlight Straight Sword.

There is a missing statue in the cathedral housing Gwynevere, which most likely depicted the adult Nameless King, and was removed when he was expunged from the annals.

Trivia

 * The Nameless King fighting alongside the Stormdrake in the first phase of the fight, is named King of the Storm; however, "King of the Storm" might be referring to the Stormdrake exclusively, as it is the one taking damage during that phase, even if its mount is attacked directly.
 * The Nameless King may be the firstborn son of Gwyn, Lord of Sunlight, the first Lord.