Dusk is a princess-sorceress from the long fallen land of Oolacile.
At some point after the destruction of her home town, Oolacile, she was trapped in a Golden Crystal Golem. Since the Crystal Golems are the results of Seath the Scaleless's experiments, it is likely that he is responsible for Dusk's imprisonment.
When the Chosen Undead visits Oolacile in the past, Oolacile is rescued by the Undead after defeating Manus. She is mentally scarred and incoherent from her experience and when the Undead visits her in the Darkroot Basin after defeating Manus, she mentions being captured and being subsequently rescued, by someone she only faintly remembers and implies it being either Artorias or the player, but she has very little recollection of what happened.