The Firstborn are the monolith aliens who have left these mysterious black crystalline slabs throughout many star systems in Arthur C. Clarke’s Space Odyssey Universe.
The Firstborn travelled the stars for a thousand years before finding the Solar System. When they arrived to Earth, the great dinosaurs had long since passed away. Their explorers saw a world swarming with life, and for years they studied, collected, catalogued. Afterwards, they began to modify and tinker with the destiny of many species, on land and in the seas. Once satisfied they left, never to return, leaving their servants the monoliths behind.
Once machine-entities, they had learned to store knowledge in the structure of space itself, and to preserve their thoughts for eternity in frozen lattices of light. Subsequently, into pure energy, they transformed themselves; and on a thousand worlds, the empty shells (their bodies) they had discarded—having twitched for a while in a mindless dance of death, then crumbled into dust. Roving, at will, among the stars, through the very interstices of space, they became Lords of the Galaxy.