Not a lore bid but for the traveller there's this theory. A ghost in the Grimoire states that the tRaveller was hit by a thousand blades. (Something close to that) Rasputin's weapon to protect earth with was a gravity spike generator which cuts like a thousand blades. So some have concluded that when the darkness was upon us Rasputin fired on the Traveller to wound it and stop it abandoning us like it did the Fallen. Basically Rasputin made it stay and fight. Due to the damage of Rasputin's attack as well as fending of the darkness the traveller went into a standby mode until it could repair itself creating Ghosts to create guardians to help the process by stopping minions of the darkness giving the traveller time to heal. True or not your guess is as good as mine but it's a neat lil theory.