My friend D*** turned me onto the Legion of Super-Heroes around 1981 or so. I became quite a fan in my teen years, especially as the mid-80s hit and then Post-Crisis with the eventual 5 Year Later Legion. I lost interest after the introductions of the clones Legionairres and the eventual Zero Hour full reboot.
It took decades, but by the early 80s we finally got actual non-human alien members of the Legion and Tellus (and Quislet) became my favorites. When they were actually used at least.
Tellus comes from Hykraius, a world very different from Earth, requiring him to wear a helmet to properly breathe.
The late great Steve Lightle created such a visually stunning character. Lightle’s run on the Legion is when I really started picking it up on a regular basis.
Apparently Tellus has returned in various reboots of the team but I had to give up caring. All of the reboots/iteration since Zero Hour have not had any staying power and ultimately end up cancelled and forgotten.
Tellus was created by writer Paul Levitz and artist Steve Lightle in Legion of Super-Heroes #9 (Vol 3) (1985)