Gilgamesh belongs to a race of "shape changers" (Gestaltwandler, Morphogenese)(not hereditary biological morphology) and he is able to change the form and size of his body within several months, which can be carried out arbitrarily during normal existence. He adjusted his body - internally and externally - to his Earth "surroundings".
Gilgamesh, whose original lifespan was 120,000 years (but is now reduced to about 50,000 years), will live here for the rest of his life. He cannot go back to his people even if he had a beamship to fly to his native planet as it no longer exists since it was destroyed in a catastrophe. All of it's inhabitants have died. It had previously existed 20 million light years away from Earth in an oval spiral galaxy known as M94, NGC 4736, discovered in the year 1781 by an astronomer named Méchain.
Gilgamesh has previously turned down an offer from the Plejaren of transportation away from Earth.
He is probably currently working as a scientist on Earth where he has access to "heavy water" which he needs for sustainment of his material form.
Gilgamesh’s people no longer exists because a sudden and unpredictable planetary catastrophe caused the whole race to become extinct within a few minutes. There were no survivors because no human beings of this people also stayed outside of the planet. Gilgamesh is, thus, the sole survivor, who has adapted his shape, however, to that of the earthly human and has morphogenetically transformed and found a new home in this world, which he no longer wants to leave.
They and their homeworld were/was destroyed. Gilgamesh is the only survivor.