The Daystrom A500 was a type of synthetic lifeform, androids created by Bruce Maddox and Estella Mackenzie at the Daystrom Institute in Okinawa, Earth at the behest of Geordi La Forge. The A500s were developed by combining Maddox's expertise in cybernetics with Mackenzie's work in bio-neural circuitry. They were not sentient, and were designed to serve as a labor force for Utopia Planitia Fleet Yards' efforts to mass produce a fleet of transport ships to relocate Romulans and others threatened by the immanent supernova of the Romulan homestar.
On First Contact Day, 2385, one of the A500s, designated F8, deactivated Mars' orbital defense system, allowing a massive attack that destroyed the fleet, the Utopia Planitia facility, and set the planet's atmosphere ablaze. In the wake of the attack, which took 92,143 lives and rendered Mars uninhabitable, the Federation instituted a ban on not just the A500s, but all synthetic life. (PIC episode: "Maps and Legends")