Tyrannosaurus is a genus of large, carnivorous theropod dinosaurs that lived in the same time period as Triceratops. Extinct naturally some 65 million years prior to human evolution, temporal anomalies in the 21st century brought about their eventual re-introduction into the wild.
The first recorded event of human-Tyrannosaurus interaction was the 2009 Third Energy Criticality Incident, when a timespace "exchange" caused by a Third Energy experiment sent a number of prehistoric creatures to 21st century Ibis Island. At least one T. rex was among them. This Tyrannosaurus killed and ate a number of humans during the night, including Cooper, a S.O.R.T. agent sent to investigate the experiment. It was revealed to have evolved to have an "obsessive" nature, persistently hunting for Regina, another agent, regardless of the many dinosaurs it could have killed and eaten. Its relentless search for Regina at one point went as far as destroying the team's extraction helicopter by attacking it, mid-air; this forced the team underground.
It made its way down a large cargo elevator, following a group of survivors attempting to collect equipment necessary for their escape plan. Reaching the bottom level, it stumbled upon Regina again, but was knocked unconscious when it damaged an electrical generator.
This Tyrannosaur was killed by the agents the following morning as they escaped the island.
No source is currently available confirming whether it was killed by a bomb explosion or in a Third Energy explosion.
In the 2050s, the Noah's Ark Plan was prepared. In order to prevent an increase in temporal anomalies from altering -or preventing- human evolution, the animals were forcibly displaced, and sent three million years into the future through an improved understanding of temporal mechanics; they were to be returned to their respective time periods once the temporal crisis would come to an end. A number of Tyrannosaurs were taken as well.
When the MTHR computer confining them in comatose conditions became corrupted, it began experimenting on the animals, turning a Troodon into a "leader" animal influencing the others. Possibly as a result of its corruption, the dinosaurs escaped and killed the human staff members, and escaping into the wild.
The genus became considerably notorious in this new world - an unrelated temporal anomaly sent a military-run city and the surrounding area to around the same time (accepting a few years leeway), providing teams of soldiers tasked with killing them. Unfortunately for the military, no T. rex was reported to have been killed, and they were considered to have no real weakness.
One Tyrannosaurus hunted Regina and Dylan Morton of a 2010 rescue team for miles in the forests against a lake, along with Edward City on the opposite side. Having lost an eye during its first appearance, it proved to be just as obsessive as the one Regina encountered one year earlier (relative to her time-frame). This ultimately led to its downfall when it stumbled into a Giganotosaurus' territory near the Missile Silo, where it was shaken like a ragdoll before being killed.
Another T. rex, notable for its pitch-black skin, was sent into Hyperspace as a result of the malfunctioning MTHR's manipulation of "Hyperspace", which was ironically causing the temporal incursions that the Noah's Ark team was sent to prevent. A Second World War fighter pilot, Mike Wired, was tasked by Dylan with shutting down MTHR and finally ending the temporal crisis. The pitch-black Tyrannosaurus first made itself known in an entire displaced city, before following Mike all the way up an active volcano. It was heavily injured in the fight with Mike, and fell into the lava.
As its crew succumbed to the effects of radiation sickness en route to a colony world, the MTHR system on board the Ozymandias was tasked with creating a new race of humans based on the crew's DNA samples. Unsatisfied with the humans' weakness to cosmic rays, it instead began culturing dinosaur DNA based on available reptile samples, and began augmenting those animals, instead. The outcome of Tyrannosaur experimentation was the Australis, a failed attempt at engineering an animal capable of surviving in vacuum.