Precursors are a race of colonizing aliens in the Pacific Rim Universe and the creators of the Kaiju. In 2013, they reopened a portal to Earth, originally established during the Triassic period, and used the Kaiju as weapons to wipe out humanity.
Precursors are spindly creatures who stand over twelve feet tall, and are capable of living for millions of years. The Precursors tried to colonize Earth during the era of the dinosaurs, but the environment proved uninhabitable for them. Millions of years later, however, the gradual pollution of the Earth made conditions ideal for them to colonize the planet.