The Traveler is a sentient, city-sized planetoid that supplies power and science to the Vanguard. Members of the Vanguard regard the Traveler with respect and some have even formed a mini-faction in honor of it, though they are stereotypically regarded as mindless worshippers and fanatics by some. Among their ranks, however, is the well-respected Speaker, who speaks for the Traveler and offers advice.
During the Sangheili reformation, the Traveler was sent with an appropriate naval escort to Sangheilios to aid in the rebuilding, as well as a large group of merchants carrying supplies.
The Traveler is believed to be incapable of being a weapon of war. It does, however, supply generous amounts of power to Vanguard planets. It is believed to have a mind of its own (thus the "sentient" classification), though the Speaker and his peers appear to be the only ones capable of communicating with it.
The Traveler helps the Vanguard by offering science in the field of interstellar travel. It provides power to the larger cities and colonies in Vanguard territory, often temporarily positioning itself over a newly founded colony. In addition, it offers the knowledge of countless star systems it has previously explored, vastly improving star charts for both civilian astronomers and the military.
The arrival of the planetoid sparked the creation of the Followers of the Traveler. Most of them are active or ex-military. The Speaker is the head of the Followers, and is regarded by Vanguard leaders as one of the wisest people among their ranks. His records are open to Vanguard officers, though he gave up most of his past when he vowed his life to the Traveler. These vows are part of the reason why the Followers are mistaken for religious fanatics.