Gwyn, Lord of Cinder

 is the final Boss in Dark Souls and one of the original lords who vanquished the Dragons.

Location
Lord Gwyn can be found in the Kiln of the First Flame.

Summoning
It is possible to summon Solaire of Astora to help in the fight if he survived in Lost Izalith. His summon sign can be found at the top of the staircase. Since the Kiln of the First Flame is a PvP hotspot, it is also quite easy to find player summon signs if online.

Family
Gwyn was the nephew of Allfather Lloyd and father of Dark Sun Gwyndolin and Gwynevere, Princess of Sunlight. He also had another, unknown son, who was the god of war and inherited the sunlight, but acted foolishly, and was promptly stripped of his deitic status.

Army
Gwyn commanded an army of Silver Knights, but then their armor was charred when Gwyn linked the flame, making almost all of them change into Black Knights. The remaining Silver Knights are guarding Anor Londo.

He also formed the Four Knights of Gwyn; the captain Dragon Slayer Ornstein; Hawkeye Gough, the leader of the Dragonslayers; Lord's Blade Ciaran and the legendary Artorias the Abysswalker.

Gwyn's friend, Havel the Rock, was also a general over his own warriors, which were presumably part of Gwyn's army.

Age of Fire
At the dawn of the Age of Fire, Gwyn discovered a Lord Soul, along with Gravelord Nito and the Witch of Izalith. With this power, he fought and defeated the dragons, along with Nito, the Witch of Izalith, his army and Seath the Scaleless, who betrayed the dragons.

When the flames began to fade, Gwyn left Anor Londo and traveled to the Kiln of the First Flame, to link the First Flame, thus unnaturally prolonging the Age of Fire. When he left, he divided his power among his children, and granted parts of his Lord Soul to the Four Kings and Seath.

Gwyn succeeded in linking the fire, but was burned in the process, being reduced from the Lord of Sunlight to the Lord of Cinder, although his soul still remained powerful.

Dashing Thrust
Used by Gwyn while he's dashing. Although it is one of his "linear" attacks, it is possible he may switch to a slashing combo midway. It is also one of his best attacks in terms of tracking the player.

Quad Slash Combo
Arguably Gwyn's most powerful attack, due to its superb speed and tracking. It begins with an angled slash, then a horziontal one, another angled and finally a horizontal slash again. The horizontal slashes have excellent tracking, however the angled ones can be sidestepped if the player moves early enough.

Kick
Rarely used, however, it causes a large drain of stamina if it connects while blocking.

Slash and Thrust
Occasionally Gwyn will interrupt his normal slash combo with a quick thrust afterwards. If it hits, the player will be stunned, leaving them open for further combos.

Slashing Upper Combo
Starts with a powerful horizontal slash, which causes a large drain of stamina, followed by two more hits. The last attack can be dodged, however.

Massive Slash
A charged slash used by Gwyn to break the player's guard.

Instant Dash/Double Slash
A very fast attack, which comes out of Gwyn's instant dash. Glides towards the player, before slashing twice.

Choke Explosion Finisher
An unblockable grab attack, which deals the most damage. It has a high hitbox, so it is possible to roll under it to avoid it. After knocking the player back, Gwyn will follow up with a jumping slash or dashing slash.