Lord Soul

A Lord Soul is a unique Soul item in Dark Souls. They are used to satiate the Lordvessel, and gain access to the Kiln of the First Flame.

Availability
Both Gravelord Nito and the Bed of Chaos drop a Lord Soul upon their defeat.

Lore
Lord Souls are the most powerful types of souls, and, along with other factors, allowed the Lords to win the war against the Dragons, thus beginning the Age of Fire.

Nito and the Bed of Chaos are in possession of a Lord Soul because both Nito and the Witch of Izalith (who was consumed by the Flame of Chaos, and was transformed into the Bed of Chaos) found a Lord Soul before the war against the Dragons, along with Gwyn and the Furitive Pygmy (despite the fact that this was in fact, the Dark Soul ).