The Protomateria (エンシェントマテリア, Enshentomateria?, lit. Ancient Materia) is a special type of Materia in Dirge of Cerberus -Final Fantasy VII-. Like the Black Materia and White Materia, the Protomateria is a special one-of-a-kind Materia created by the Lifestream that lets the holder tap into the power of Chaos and Omega, and ultimately holds the balance between the salvation or destruction of the planet of Gaia in grave times.
The Tsviets sought the Protomateria to control Omega, and by uploading the memories of Lucrecia Crescent into Shelke the Transparent, discovered it was held by Vincent Valentine. They attacked Vincent several times, demanding the Protomateria, but he was unaware of what they meant. Eventually, in the Shinra Mansion, Rosso the Crimson attacks Vincent from behind and seizes the Protomateria from inside his chest. At this time, Vincent transforms into Chaos without warning.
At this time, the connection between Vincent, Chaos, and the Protomateria is explained. The Protomateria allows the holder to access the power of Omega or Chaos. When Chaos was implanted into Vincent and began to grow out of control, Lucrecia implanted the Protomateria into Vincent's body to save him. Therefore, Vincent needs the Protomateria to control Chaos, and without it his mental defenses are weakening and he is losing control to Chaos.
Using the Protomateria, Weiss the Immaculate, under Hojo's control, takes on the power of Omega. However, Shelke manages to return the Protomateria to Vincent and Vincent goes on to defeat Weiss and Omega using Chaos.
Proto- is an English prefix meaning "first".
Materia is a Latin term meaning "matter" or "substance", probably from the phrase materia magica (materials for magical rituals). It is also the Italian, Spanish, and Portuguese for the word "subject" and "matter".