The Old Ones are the four ancient ones possessing the four Great Souls in Dark Souls II. The Great Souls are guarded by the four main bosses of the game: the Lost Sinner, the Old Iron King, The Duke's Dear Freja and The Rotten.
According to Sweet Shalquoir, the Old Ones are said to be so ancient that even their names have been forgotten. The Emerald Herald implores the Bearer of the Curse to seek them out and gain the power of their souls in order to reach Drangleic Castle and thus King Vendrick.
After their defeat, Shalquoir gives additional information regarding the Old Ones.
Old Iron KingEdit
The Old Iron King, after being killed by the Smelter Demon, is said to have hurled himself into the flame, becoming Ichorous Earth. This is a reference to how Gwyn, Lord of Cinder hurled himself into the First Flame to link the fire and prolong the Age of Fire. Second playthroughs and onward cause the Old Iron King to drop the Old King Soul upon defeat.
The Lost SinnerEdit
The Lost Sinner, imprisoning herself in The Lost Bastille, was said to have attempted to light the First Flame. In the same manner, the Witch of Izalith attempted to recreate the First Flame using her Lord Soul, but instead created the Flame of Chaos. As well, a creature similar to a Chaos Bug can be seen crawling into the eyehole of her mask in her introductory cutscene. Pyromancers, perhaps references to the Daughters of Chaos who were the progenitors of Pyromancy, aid the Lost Sinner from NG+ onward. Playthroughs past the first one will reward players with the Old Witch Soul.
The Rotten, found below the Grave of Saints and The Gutter, is composed of the bodies of numerous Undead. This is similar to the manner in which Gravelord Nito is composed of numerous skeletons. Upon defeat from NG+ onward, he drops the Old Dead One Soul alongside his own.
The Duke's Dear FrejaEdit
Unlike the other bosses, it is implied that Freja is not an Old One, as she does not reward the player with a Great Soul upon her defeat. Rather, the Great Soul is found under the corpse of the great dragon behind her, the Writhing Ruin. However, Manscorpion Tark's dialogue implies that his creator and master was a being similar to Seath the Scaleless, and further refers to Freja as his master after her defeat. He implies that his master never truly dies, but rather changes shape and never releasing his grudge. The Duke's Dear Freja, from NG+ onward, drops the Old Paledrake Soul.