Precursors are a race of colonizing aliens from the Anteverse 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 try to wipe out humanity.
Precursors are spindly creatures who stand over 12 feet tall, and are capable of living for millions of years (partially because time flows differently in the Anteverse). Their appearance is akin to that of an aquatic insect. They have translucent wings and shell-like bodies that reveal their internal system. They have elongated, crest-like heads and protrusions that stem from their heels, and small, opal eyes that are reminiscent of the eyes of a shark.
Concept artists, Wayne Barlowe and Keith Thompson finalized their design to suggest a type of clerical hierarchy that typifies the fashion and culture of pre-revolutionary French nobility. Depending on the designs, Precursors were given the ranks of "Cardinal", "Bishop" and "Ambassadors". Their ranks are reflected in the design of their wide and flat crowns.
Precursor civilization relies heavily on bio-mechanical implements. They live inside large towering formations that are part of the environment and they use cages to maintain the cloned Kaiju.
The Precursors tried to colonize Earth during the era of the dinosaurs, but the environment proved uninhabitable for them. Millions of years later, humanity's pollution of the Earth made conditions ideal for them to colonize the planet.
August 10, 2013, the Precursors created the Breach to send the Kaiju to destroy humanity. The Precursors' plan to colonize the Earth was to send Kaiju in waves. The first was the shortest period that lasted from the first Kaiju appearance in 2013 to 2014.
The second phase is long-term, an eight year period that was essentially a standoff between the Precursors and Kaiju against mankind. The third and final phase began in 2024 and would end with an extinction event of the human race.
The Precursors' extinction event began with the Double Event, an occurrence that brings two Kaiju, Otachi and Leatherback, from the Anteverse through the Breach to Earth. K-Science officer Hermann Gottlieb predicted that the throat of the Breach is continually expanding to accommodate the Kaiju the larger they became.
When Newton Geiszler Drifts with the Kaiju's brain inside the K-Science Lab, he caught a glimpse of the Precursors' true intentions and their relationship as the creators of the Kaiju. In doing so, he revealed information to the Precursors that left the Defense Corps' Jaegers, Cherno Alpha and Crimson Typhoon vulnerable to the specific strengths of Otachi and Leatherback when the Kaiju attack the Port of Hong Kong.
The second Drift he initiated with the Baby Kaiju's brain, prompted the Precursors to hasten their creation of Slattern. Beforehand, they send Raiju and Scunner to guard the Breach from the approaching Jaegers, Gipsy Danger and Striker Eureka.
When Raleigh Becket abandons Gipsy Danger to destroy the Breach, three Precursors within the creation facility glimpse the Jaeger as it descends into their universe. They and the Kaiju were killed when Gipsy Danger self-destructs. The resulting explosion destroyed the Kaiju creation facility and collapsed the Breach.