I believe Osiris is the one that will show us the true nature of the traveler/speaker, I think we'll have to find him first and then at the end of the Vex DLC he'll tell us that the traveler caused the collapse and brought the darkness, then the cabal DLC after that will consist of us going to the Cabal homeworld to steal a very specific type of bomb from their emperor that will be able to destroy the traveler.... end of Destiny 1