Lord Aldia is King Vendrick's elder brother. He aided his brother in founding the kingdom of Drangleic, but he then secluded himself in his manor, searching for the secrets of life, viewing the Undead as the key to finding it. Through his experiments, Aldia sought to learn the nature of the undead curse, and to shed the yoke of fate.
Due to a dispute on the research of souls, or the research methods on how to end the Curse, Vendrick locked Aldia away in his keep. It was there that Aldia "kept Giants in his manor, and attempted to recreate a dragon, but after some time, was not heard from again".
With the release of Scholar of the First Sin, it is revealed that Aldia did not become the Ancient Dragon, but was transfigured into a blob-like creature that appears to be composed of fire, witchtree branches and a glowing red eye. He will appear to the player at the the last Primal Bonfire they reach, the entrance to the Undead Crypt and the Dragon Shrine. If spoken to in all of these locations he will become the final boss after defeating Nashandra at the Throne of Want.
His dialogue ranges from benign to going as far as to express outward rage at Gwyn, Lord of Cinder, who is referred to by Aldia as the "Lord of Light". The scholar describes how the old Lord of Sunlight expelled the darkness, and began the cycle of light and dark. This cycle, this curse, forced men to assume a fleeting form, reverting them back to their hollow form. They became less than what they were, and to Aldia, this is the first sin he has taken his name from. He claims that men are mere props, and that no matter how exquisite, a lie will remain a lie. The anger is audible in his voice at this point, an expression of his fury at the commitment of the first sin, the first linking of the flame.