The Traveler's species
The Traveler's species were a technologically advanced humanoid species native to the planet Tau Alpha C.

History 
This technologically advanced species wanted to help Earth survive its early technological age. To this end, around 3000 BC, they took certain Humans to serve as the forebears of a pool of genetically-perfect Earth operatives. As Gary Seven, one of their Class 1 supervisors, said on Earth in 1968: "A truly advanced planet wouldn't use force. They wouldn't come here in alien forms. The best of all possible methods would be to take Human beings to their world [and] train them for generations until they're needed here." 

These agents were Human but flawless in design: not even the Vulcan nerve pinch could stop them. They were transported back to Earth as needed by means of an incredibly powerful transporter beam which, in the one case where it hit the , shook the vessel violently and locked her circuits wide open (fusing those having to do with recording). At least one agent was accompanied on the interstellar beaming by a humanoid who preferred to appear to be a domestic cat (or vice versa). 

Gary Seven followed two agents dispatched to Earth, 201 and 347, on the day in 1968 when there occurred a major assassination, an Asian coup d'etat, and the launch into orbit of a US nuclear weapons platform. Seven came because the agents, dead in an automobile accident, had been incommunicado. He took over their assignment – which was to effect a misfire and near-holocaust to frighten the USA and the other major powers out of their foolish "balance of power" strategy – and completed it by the skin of his teeth. ()

One of their representatives, The Traveler, was encountered by Starfleet on at least three occassions during the mid to late 2360s. 

According to Starfleet records, the Traveler was from Tau Alpha C, a planet the inhabitants of which were known to the Enterprise computer. () When, in 2367, Beverly Crusher tried to find him or another from his race, she directed the ship's computer to first search for inhabitants of this planet, and then try to reach the planet. () A few years later, and while under a state of distress, Crusher described the Traveler as being from Tau Ceti. ()

Physiology 
Travelers had exceptional abilities based on their perception of time, space, and thought, which endowed them with exceptional implications in propulsion, which The Traveler claimed others of his kind also possessed. () 

Physically, the Traveler's species had a pronounced brow line and nose bridge, as well as three large fingers on each hand. 

According to The Traveler, this species had not sought contact before this time because before that, because [the Federation cultures] had been deemed uninteresting and not meriting serious attention. The Traveler himself described himself as exploring "[our] reality" ()

Appendices

Appearances

Background information 
With the help of Bob Justman on the Traveler's "mental makeup", actor Eric Menyuk took it upon himself to help create the alien Traveler, while falling within the guidelines of the producers wanting "someone who was definitely alien but had very human characteristics that weren't going to scare people. There was no premise." With Menyuk's input, the physical makeup was designed by Michael Westmore, "We came up with some ideas about what the character should look like. We didn't want to make him ugly, something people didn't want to look at." Once designed, the first go with the makeup application took three hours to apply and by the end of the week, Westmore had reduced that time to two hours and 15 minutes. According to Menyuk, "The makeup was so comfortable that I would forget I had it on." (, December 1988, Issue 137, p. 54)

For the Traveler's hands, special latex gloves were made that could be simply slipped on and off before and after takes. (, December 1988, Issue 137, p. 54) A pair of these latex hands were later sold off on the It's A Wrap! sale and auction on eBay. 

Unnamed species