The Indominus rex (or I. rex for short) was a new attraction in Jurassic World. The hybrid was created by combining the genetic traits of multiple species. Some of the known species that were used in the creation of the hybrid are Tyrannosaurus, Velociraptor, as well as modern animals like cuttlefish and an unspecified species of Tree frog. He served as the main antagonist of the 2015 film, Jurassic World.
Two I. rex were meant to be kept in their own paddock that had 12 meter (40 feet) high walls. This was also planned in case one of them died. However, the older Indominus cannibalized her own sibling before it even hatched, and would also attack the workers of her paddock as well. Three weeks before their paddock was open to the public, Simon Masrani told Claire Dearing to consult Owen Grady to see if he was interested in taking a job requiring him to inspect the Indominus rex Paddock for any vulnerabilities after seeing her attempt of breaking the glass in the observation deck.
That same day, the Indominus later managed to avoid her temperature being picked up by the thermal cameras thanks to the frog DNA in her species and left claw marks on the walls to make them think she was able to climb over the enclosure wall. When Owen Grady, paddock supervisor Nick and worker Ellis came in to investigate the damaged paddock, the hybrid ambushed them as soon as they got word that she was still in the paddock, making a quick meal out of Ellis in the process. As they fled, she managed to break through the door as it was not fully shut. Free at last, the I.rex managed to detect and eat Nick, but Owen evaded her by hiding under a nearby crane outside of her paddock and then cut the crane's fuel tank, masking his scent. The Indominus rex then headed off into Jurassic World park, attracted by the thermal signatures of the visitors there.
Her escape was not reported to Jurassic World visitors because Simon Masrani thought the Asset Containment Unit would capture her by following her tracker implant. The I. rex traveled south of her paddock having detected the thermal signatures of the visitors in Main Street. She managed to claw out her tracker, along with some flesh still attached to it, and ambushed the team as soon as they arrived, killing most of the troopers, including Katashi Hamada, Craig, and possibly other members of the team, convincing Owen that the island needed to be evacuated. She then went near the Gyrosphere attarction and attacked brothers Zach and Gray Mitchell who were observing 4 Ankylosaurus. In her attack, she agitated one of the Ankylosaurus who proceeded to fight back against her though her counterattack ended with her being killed by the Indominus via rolling her onto her back and breaking the neck. She resumed attacking the two brothers by piercing her mid talon into the glass and rotated the vehicle so the boys could see their demise. She then attempted to chomp the gyrosphere whole but got her mouth stuck, but attempted to smash it several times into the ground to crack it open, but the two brothers escaped by getting out of their damaged Gyrosphere and jumping off a waterfall. She gave out a loud roar in disappointment and headed to the Gyrosphere Valley.
Shortly afterward, the Indominus attacked a herd Apatosaurus, killing five and fatally injuring one before moving on into the restricted area of Isla Nublar, leaving their bodies uneaten. While in the restricted area, the I. rex discovered Owen Grady and Claire Dearing inside the Visitor Center to which she took the opportunity to attack and chase them after pretending not to notice them and breaking through the ceiling in a jumpscare-like fasion. However, her pursuit of the humans ended when she saw the JW001 piloted by Masrani outfitted with a heavy machine gun in pursuit of her. She led her pursuer to the Jurassic World Aviary where she smashed through the enclosure's walls and scarred the pterosaurs inside out of the aviary to the open hole she created. As the freed pterosaurs lead to the destruction of JW001 and attacked the guests in Main Street, the Indominus traveled further into the restricted area of the island.
That night in the restricted area the members of Jurassic World's Velociraptor pack found her. However, she communicated with the raptors and became the alpha of their pack. As the leader of the pack, she commanded the raptors that were under her control to attack the humans that came with them and were in the area, to which they followed this order. Upon the initiation of this order, the InGen Security troopers, Owen, and Barry, who were following the Velociraptors opened fire on the hybrid. She managed to escape the brawl the firefight that ensued as the small arms fire had little to no effect on her, but she did nearly collapse on the ground when she was hit by rocket from one of the troopers while escaping.
The I. rex finally arrived in Main Street where she met Owen, Claire, the Mitchell brothers and the three remaining raptors once again, commanding the raptors to finish them off. With Owen's attempt to regain Blue's trust by removing her camera a few minutes ago, she decides to make him the alpha again. Blue then screeches at the I. rex, who responded by knocking her into a wall, seemingly killing her. The raptors, now aligned with Owen's group again, proceeded to attack the Indominus while Owen Grady provided suppressive fire with his rifle. But the fight ends fairly quickly as she easily kills Echo by tossing her into a grill that engulfs her in flames and Delta by snatching her into her jaws and throwing her away. With the raptors defeated, the Indominus rex then proceeds to resume hunting Owen and the Mitchell brothers who are huddled inside one of Main Street's shops. She nearly drags Gray to her but is stopped by another dinosaur who challenges her: Rexy, Jurassic World's Tyrannosaurus rex.
Rexy carries out a heavy assault on Indominus, but Rexy is overpowered by the hybrid. The Indominus almost delivers the killing blow before she is then attacked by Blue who is still alive from the onslaught. This allows Rexy to return to her feet and grab the I. rex by the neck, pushing her into many of Main Street's buildings, all while Blue continues biting and scratching her. Finally, she is flung to the edge of the Jurassic World Lagoon where the Mosasaurus there detects the hybrid and proceeds to pull her under the water, presumably eaten alive or drowning if the bite force of the Mosasaurus did not kill her first.