The Traveller was a mysterious humanoid from Tau Alpha C who had the ability to alter time and space with his thoughts. It is implied that these abilities are from his understanding of the concept that "matter, energy, and thought" are related and interchangable. His name is completely unpronounceable by Federation standards.

The Traveller first appeared in 2364 as an assistant to Starfleet propulsion expert Kosinski, who claimed to have discovered a revolutionary new method of warp drive. Kosinski's formulas turned out to be bogus, as Wesley Crusher discovered that it was actually Kosinski's assistant, the Traveller, who was the driving force behind the propulsion method. Things went astray, however, and the USS Enterprise-D was catapulted millions of light years from its previous position into the M-33 Galaxy. Later, while attempting to return to their home galaxy, the Enterprise instead traveled too far, winding up a billion light years in the other direction from home. The Traveller collapsed in exhaustion and was taken to sickbay, where he revealed the secret of his abilities. He eventually returned to engineering, where he helped return the ship and crew home to the Milky Way Galaxy.

The Traveller noticed something special about the young Wesley Crusher, comparing him to a young Mozart. Inspired in part by this, Captain Picard promoted Wesley to an acting ensign in the traditions of Starfleet. The Traveller played a significant role in the destiny of Wesley Crusher.

(TNG: "Where No One Has Gone Before")

The Traveler in 2370

The Traveller was next encountered by the Enterprise crew in 2367, after a "warp bubble" experiment by Wesley Crusher went awry, trapping his mother Beverly Crusher in her own universe. The Traveller appeared and directed the crew on her rescue. He did not solve the problem himself; instead, he urged Wesley to concentrate his own thoughts in order to facilitate the rescue. They succeed in rescuing the elder Crusher, while the younger Crusher continued his maturation.

(TNG: "Remember Me")

In 2370, The Traveller appeared incognito as Lakanta, a villager on Dorvan V, to Wesley Crusher. Lakanta, who seemed to have intimate knowledge of Wesley, directed him to seek the answers to his troubled destiny. Wesley was, at the time, quite uncertain about his future in Starfleet. The Traveller guided Wes to the "habak" where Wesley had a vision of his deceased father telling him that his destiny lay somewhere other than with Starfleet. The cadet heeded the advice and resigned from Starfleet, after which The Traveller revealed his true identity, and promised to mentor the young man on his new journey, presumably to other planes of existence.

(TNG: "Journey's End")