For most of the millions of years of its existence, the planet Mercury, closest to the Sun, was a dead, sun-baked world, pock-marked by meteorites and scorched by occasional flares. With hardly any atmosphere, and therefore no weather, its rock-formations remained hard, cold, sharp, and unchanged.
But there was life, underground, beneath the windless horizons haunted by the flaring 'ghosts' of the sunset. In the bitter-cold caves and hollows of Mercury, lived simple organisms, microscopic in size and uncountable in number, fed and bred upon heat alone, and the few choice minerals whereof they built their bodies. Not for them, the pitiless sun and bitter cold of Mercury's surface; they lived in the darkness, and grew, and evolved in it.
These microbes were highly intelligent: a fact not appreciated when humanity annexed Mercury, with the terraforming equipment derived from the mysterious, space-borne archive, known as the Traveler. Armed with this equipment, and its godlike powers, the human race changed Mercury into "a garden world, full of gentle things", under a heavier, denser sky. Of the indigenes, humanity took no notice, except to name them, 'Radiolaria', after a similar class of life on Earth, and erect stations to study them. But the radiolaria, so called, took long, slow, and deliberate notice of these invaders, and studied them in return.
How quickly they learned, and how much, is difficult to believe, even afterward, when the radiolaria emerged, clad in new bodies, and wrought havoc on their own world, and on all the worlds beyond. No longer microscopic and subterranean, they now marched across the surface in anthropomorphic housings of steel, with weapons of plasma and heat, and brought death and destruction wherever they went. Not content to reclaim their own world, they were determined to conquer the solar system, and make every world and all space into a distorted likeness of the cooler, darker realm of their origin.
To that end, these rebels against the dominance of multicellular life, mastered sciences above and beyond the means of their enemies: perpetual motion, antigravity, matter-to-energy conversions, and even time-travel. In pursuit of their ultimate purpose, the new cybernetic intelligence changed their entire planet into an immense super-computer, intended to represent, exactly as in reality, the end of all their labor, every possible means of its attainment, and every obstacle, success, and failure imaginable.
Earth's scientists saw them; Earth's military resisted them; Earth's far-flung colonies sent allies against them; and in time, Earth's historians bestowed a name on them: a name most fitting to a persistent, and perhaps ineradicable nuisance.
They were called, the Vex.