Praedyth

Praedyth was a Warlock who had been part of Kabr's fireteam during their assault on the Vault of Glass. Praedyth himself was believed to be a myth; Praedyth's Timepiece and Praedyth's Revenge are the only pieces of evidence of his existence, until the Vanguard discovered a message coming from the Vault.

His fate is explored in the Story Mission Paradox. After fighting through Taken, the Guardian discovers Praedyth's corpse, long dead, trapped deep within the Vault of Glass.

If a secret area in the Paradox mission is triggered as the Daily Heroic, it is revealed that Praedyth still exists as a ghost, and that he originally worked for the Future War Cult using a custom made Ghost shell, known to players as the Intrusion Shell. His ghost implies that they were one of the first to discover Oryx's power to Take through what would eventually become his transcendent powers, as she (his ghost) claims she saw the Darkness "wear a Fallen Captain like clothes," implying that it was Taken.

Quotes

 * "Praedyth's fall isn't over… because it hasn't happened yet… and it will happen again."
 * "He skipped like a stone on time's ocean. This is what's left." - Unknown
 * "So the Vex have predicted their own annihilation. When did they believe this would happen? Can calculations of minds the size of planets be wrong?"
 * "I had a friend, back at the Tower. she used to say. 'Praedyth, there's always room in the back of the mind for hope. It's the crack that let's the light in.' The Vex have no hope. No imagination, no drive, no fear. All they have is the Pattern. Everything must fit. If it can be made to fit, good. If it can't, it gets cut away."*
 * "They think this is the end of them, a path with no escape. And yet here they are, and there they were, and there they will be, and there they will have been. For them, there is no paradox. There is only the pattern. And the pattern needs the Vex to see it to completion. And so the Vex must be. For the mind of the Vex, is that faith?"
 * "Welcome to the end of the Vex. Their "immutable" future."
 * "Enslaved to a will they don't understand. A will long dead here. Dead eons ago. But then they won't end, will they? Because you're here."
 * "The Vex won't spare the City. They won't even thank you. But that's the thing about Light. You never know where it will shine."

Trivia
In one Quest Item, Talk to Lakshmi-2, Praedyth states he can see, in every single Vex timeline, the Exo Stranger.