The Thorian, also called Species 37, is an ancient sentient plant at least fifty thousand years old – its ability to hibernate for thousands of years makes its real age impossible to guess. The Thorian is a unique creature with mind-controlling and telepathic abilities, and a massive sensory network. It releases spores into the air that allow the Thorian to control those who inhale them, using pain to control their behaviour. These ‘thralls’ then tend to the Thorian and obey its will.
Commander Shepard first hears of the Thorian from Lizbeth Baynham, who tentatively suggests that it might be why the geth are attacking the colonists on Feros. Once freed from the Thorian, Shiala then tells Shepard its history.
According to Shiala, the Thorian existed on Feros long before the Protheans arrived. It would spend thousands of years in hibernation, then awake for “a few frantic centuries” of activity before resting again. When the Protheans arrived and began building the metropolis that would eventually cover Feros, the curious Thorian studied them, likely made several of them into its thralls, and even absorbed them after they died, allowing them to become a part of its expanding consciousness.
From the Protheans, the Thorian’s mind gradually absorbed the knowledge that would form the Cipher. The Thorian survived the cataclysm that destroyed the Protheans, and continued to grow across Feros for the next fifty thousand years.