Camperian

"This year we lost the planet Camperia."
"Stop telling people we're dead!"
"Sometimes, we can still hear their voices."

— An adaptation of a common conversation around this topic

The Camperians were a species of intelligent humanoids with a lot of power in regards to energy absorption and manipulation. They were also power hungry jerks who tried at several points through the millennia to take over the galaxy. They always failed, for one reason or another.
Eventually, they were wiped out, with particular care to eliminate every trace of their species.
Or at least, that's what various galactic governments like to claim. The reality is that there's actually quite a few of them around, particularly on Earth since there's a physical resemblance so they can blend in really well.
Aside from a few variations of internal organs, they look like humans. The primary difference comes from their abilities. They absorb energy from various sources, store it up, and then release it in a particular way. Different people could manipulate different energy. Like some people could absorb and emit kinetic energy, while others focused on magnetic forces, or perhaps heat, or light. The specifications as to why this worked the way it did are unclear. But always a flow of energy, coming in and then going back out.
The main thing is their sensitivity to telepathy. They're apparently insanely easy to read and to control, but only for a very short time before they essentially have an allergic reaction and their brain swells and they die. So ultimately their desire to take over the world was thwarted quite simply.
The thing about Camperians is, you're not supposed to acknowledge it if you find one. There are some planets where they could just about blast your face off and no one would admit to them being Camperian. Wiping them all out was "a thing" and to deny that it worked is just about heresy.