Seath the Scaleless

 is a boss in Dark Souls

Location
Found first in the The Duke's Archives and then in the Crystal Cave.

Plot
The Chosen Undead must confront Seath in order to retrieve his Bequeathed Lord Soul Shard and satiate the Lordvessel.

Lore
Seath, being albino and scaleless, likely resented his brethren for possessing stone scales of immortality, thus leading to his betrayal. He was granted Dukedom by Gwyn, Lord of Sunlight for his role in defeating the Everlasting Dragons. During his time as Duke, he began to research the scales of immortality in order to acquire that which he lacked, though was driven mad by his research.

He commands the Channelers who traveled to far off lands in order to collect suitable human specimens, amongst these were countless maidens, for his experiments. The purpose of these experiments is presumed to be related to the discovery of immortality, but hordes of "mistakes" were created in the process.

Seath, who is blind, is said to be the grandfather of Sorcery and is the object of Logan's obsession.

Strategies
Staying at his side makes it easier to stay out of the area of effect of his breath attacks, and he won't be able to hit with his claws or tail as easily.

It is also possible to use only a bow against Seath with great success. Get a good distance away from him and it is possible to get 4-5 shots in before he gets too close. The only real danger in this strategy is when running past Seath to gain some distance.

Attacks
Seath uses multiple breath attacks, which cause crystal stalagmites to shoot forth from the ground, and increase your curse build-up. The build-up is lessened when you block.

His first attack is a forward breath attack, which can be dodged if seen coming. He will lean his head back before he uses this ability. For the second breath attack he breathes around himself in a large semi-circle, for which you simply have to block and run out of the area of effect. After going below 50% health, Seath will use an AoE attack with a large range that spreads crystals in a perfect circle from him. A bluish white orb of light will appear as he charges this attack, and he will roar as it starts, leaving the player a fair amount of time to get the hell away before it happens.

He also will attack you with his claws if you get close enough, or his tail if you try to get behind him.