Refusian

Refusians were the original natives of Refusis II. They welcomed the humans and Monoids to their planet, so long as they ceased to be in conflict with one another. When the First Doctor suddenly turned temporarily invisible, Steven Taylor thought that it was caused by contact with Refusians.

The Refusians once had physical form. A giant solar flare caused the Refusians to lose these bodies, and as a result, they no longer have a recognizable "being". The Refusians are not only invisible to other races, they are invisible to one another; they can only sense another Refusian's presence. In their new forms, the Refusians are super-strong and can move heavy objects as if they were practically nothing. They are also an advanced race, possessing various weapons that seem to have a wide range of capabilities, from stunning Monoids to blowing up landers, without even being seen to operate.

Despite their newfound talents, the Refusians missed seeing signs of life on their planet. Once they became aware of the Ark's journey to Refusis II, they welcomed it, and began constructing a city in which the humans and Monoids could live. They were dismayed to see the fighting between and among the groups when they arrived on Refusis, and agreed to help the Doctor defuse the situation. Once the humans had been saved from destruction, and the Monoids had quit fighting, the Refusians ordered them to begin living together in peace if they wanted to stay on the planet successfully.

(DW: The Ark)