This is the traveller, he is an inventor from Earth but in an alternate reality, his Earth was destroyed by a race known as the Slobbithians.
The traveller is unable to age due to an incident that occurred whilst he was inventing the S.T.A.R. Shifter. The time circuits were damaged which exposed him to the pure Chronolite contained within causing his age to become time-locked.
After his planet was destroyed he started traversing the multiverse to acquire wisdom so that he could prevent any repetitions of what happened to his planet.
The traveller prefers to go by the name "T" as it is easier to say than "traveller. He loves all planets and lifeforms but has a particular soft spot for Earth-like planets.