The traveler is the husk of a fallen empire dedicated to protecting innocence and life in the universe, beaten and destroyed by countless barbaric and warring and belligerent alien races. The traveler was named thusly because of it's endless retreat until it found a planet housing races of equal idealisms and hope, there it made it's stand with it's new children and died protecting them. Thus the traveler ended its days of traveling and can only be remembered by those who survived and likewise seek out those who cannot protect themselves.

Oh hell man, use your imagination. The Traveler is a time-traveling sentient mechanical organism and a remnant of an ancient civilization lost and gone for billions of years. There... see what stories you can cook up based on that.