Osiris

"If I don't stop the Vex, there won't be anything to come back to."

- Osiris

Osiris is an old Warlock and a former Vanguard who was exiled from the City.

Early history
A veteran of Six Fronts, Osiris was a well respected warrior whose prowess at that battle convinced Saint-14 to recommend him to the Speaker as Vanguard Commander. He had also served as the Speaker's apprentice for a time. However, his desire for truth about the purpose of Guardians and the nature of Darkness drove him to madness. His theories were not only considered borderline blasphemous, but he was also diverting Guardians and resources away from protecting the City and refugees, and towards chasing legends and rumors, such as the Vault of Glass; it's implied that he was the one who inspired Kabr, the Legionless into going into the Vault. He studied the Hive, in particular prophesying the coming of Oryx, and is also rumored to have come "too close to understanding the Vex".

His obsession with the nature of the Darkness and misuse of resources eventually drove the Speaker to exile him, as the Speaker believed he had become as obsessed with the Vex as Toland, the Shattered had with the Hive. He is described as having a cult of personality, and has a number of disciples, such as Brother Vance, who attempt to see how far the Light can be bent before it can be broken. Osiris himself seems to have vanished, even from those who follow him, some claiming that he is at once "alive and dead."

Destiny
Whether before or after his banishment, Osiris held council with the other two powers of the Solar System, the Queen of the Reef and The Nine. His arrangements with the Queen extend to his followers, explaining their presence in the Vestian Outpost. He also receives reports from Eris Morn and has employed the Sunbreakers to work for him.

The Disciples of Osiris held a Crucible tournament in his honor called the Trials of Osiris, where they sought to recruit the toughest Guardians to their cause.

Destiny 2
In Destiny 2 in the Adventure Deep Conversation, Osiris makes contact with Ghost through the Vex network to send his regards.

Curse of Osiris
Osiris finally appears in-person and serve as a central figure in the DLC, Destiny 2: Curse of Osiris. Having returned after years of exile, Osiris makes contact with his former student, Ikora Rey, informing her that the Vex from both past and future timelines are amassing on Mercury. Though distrustful of her former teacher, knowing his dangerous ideals nearly destroyed the Vanguard, she sends the Guardian to find him and determine whether he will be a powerful ally against the Vex or a dangerous enemy.

Quotes

 * "Crota's spawn will snuff out the worlds of Light, and Oryx's coming shall be unfettered."
 * "Every end crawls from the same pit, rising from the schism to swallow matter, Light and life. It cannot be stopped, but here, it can be slowed. The Shrines of Oryx must be destroyed."
 * "If the Vex succeed, it's the end of everything."

Trivia

 * Osiris is presumably named after the god of the same name, the Egyptian god of the afterlife, the underworld and the dead.
 * Osiris was intended to appear in the original storyline of Destiny. He would act as a mentor to the player, and be found in an ancient Vex temple on Mercury. He was accompanied by a robotic assistant, who would later be re-purposed as The Stranger.
 * The same voice actor for Osiris,, also voiced the narration for the Pathways out of Darkness ViDoc. It is unconfirmed if the narrator is supposed to be Osiris.
 * Osiris was the name of a Guardian Faction during the game's pre-alpha phase. It appears that it has been changed to the Cult of Osiris, though it is not a faction that can be joined as of yet.
 * Before being named Vanguard Commander, the Concordat claimed to have records proving Osiris was a Golden Age experiment mis-incarnated as a human by an inept Ghost. Whether this is true or not, is unknown.
 * Due to his reputation, nearly every Vanguard veteran has a poor opinion of Osiris. Saladin expressed disdain towards him for nearly ruining the Warlock Vanguard and even his former student, Ikora, has called him the most notorious Guardian in Vanguard history.

List of appearances

 * Destiny
 * House of Wolves
 * The Taken King
 * Destiny 2
 * Curse of Osiris