President Koopa is the primary antagonist of the live-action Super Mario Bros. movie. He is based on the video game character Bowser, but only loosely as his character differs extensively in the film. Whereas the King Koopa of the Mario games is a fire-breathing turtle, this version of Koopa is a humanoid descendant of the tyrannosaurus rex. Aside from his animosity toward Mario, this iteration of Koopa has almost nothing in common with the Koopa of the video games.
65 million years ago, the dinosaurs were believed to have been destroyed when the Earth was struck by a meteorite. This was not the case, however; the meteorite's impact somehow created a parallel dimension where the surviving dinosaurs continued to thrive and eventually evolve into intelligent, sapient beings resembling humans.
In the modern era, the dinosaurs' dimension, now known as Dinohattan, was suffering from a lack of resources and was heavily polluted. The power-hungry Koopa had overthrown the King of Dinohattan and appointed himself as President, reshaping the city in his image. In order to salvage the city, Koopa attempted to merge his world with the human world by acquiring the Rock, a fragment of the original meteorite that had split the world into separate dimensions in the first place, and reintegrate it with the meteorite. However, the merger could not be carried out by just anyone; only members of the royal family could withstand the awesome energies of the meteorite when the Rock was reinserted. Since Koopa had de-evolved the former king into fungus, that left only the queen and her offspring, which had yet to hatch. The queen had taken the Rock and her infant's egg through the dimensional barrier to Brooklyn, New York. She would die soon after when a cave-in occurred near the portal exit, which would seal off Dinohattan from the human world for the next two decades.
23 years later, the dimensional breach was blasted open again during an excavation. Koopa sent his dim-witted cousins Spike and Iggy to Brooklyn in order to find Daisy, the daughter to the former king and queen, who was in possession of the Rock and was needed to carry out the dimensional merger. With no real means of identifying Daisy, however, the two minions abducted several innocent women before they found their mark. Daisy, who was the head of an archaeological dig located near the portal, was trying to repair a damaged water pipe with the help of two plumbers, the Mario Brothers. Iggy and Spike grabbed Daisy, but Mario and Luigi chased after them and Luigi grabbed the Rock around Daisy's neck.
Koopa soon had Daisy in his clutches, but without the Rock he still couldn't merge the dimensions. Iggy and Spike told Koopa that a pair of plumbers had taken the Rock and so Koopa issued an alert to the Dinohattan police to find them and bring them in. Soon enough Mario and Luigi, who had followed Spike and Iggy through the portal, were found within the city and brought before Koopa, but the Rock had been stolen. Koopa decided to introduce the brothers to his Devo Machine, a device that forcefully de-evolved its subjects. Mario and Luigi were able to escape, however, and before they fled Mario strapped Koopa into the seat of the Devo Machine and activated it. The machine was shut down before it finished the de-evolution process, but as a result Koopa began to take on more obvious reptilian traits. Occasionally his face would morph, becoming partially scaly, or his tongue would extend and his eyes would become slitted like a reptile.
With the Mario Bros. and the Rock missing, Koopa once again dispatched Spike and Iggy to find them. First, he subjected his cousins to the Devo Machine which had been set to 'Evolve', allowing Koopa to enhance their brains and make them smarter. The duo later returned to Koopa Tower, but had allowed the Marios to sneak in after helping them retrieve the Rock. However, the Rock was stolen by Koopa's treacherous secretary and mistress Leena, who believed that Daisy wasn't necessary to bring about the merger and attempted to re-awaken the meteorite herself. Whilst Mario and the other kidnapped Brooklyn girls struggled to escape from Koopa's lair and confronted the dictator on the streets of Dinohattan, Luigi and Daisy tried to stop Leena, but failed. Leena succeeded in reinserting the Rock into the meteorite, but a backlash of energy killed her in the process.
With the meteorite restored, the dimensions began to merge. Koopa and his Goomba soldiers appeared in Brooklyn and Koopa attempted to de-evolve Mario using a Devo Gun, but Mario shielded himself using a mushroom he had taken from a fungal growth which grew in his hand, protecting him. Koopa's and Mario's fight would be taken back to Dinohattan when Daisy and Luigi removed the Rock from the meteorite, reversing the merger. Luigi then joined Mario in fighting against Koopa and the brothers used a pair of stolen Devo Guns to de-evolve Koopa. At first, Koopa was de-evolved into a tyrannosaurus, but another blast from the Devo Guns reduced him to primordial ooze which splattered onto the street. With Koopa gone, Dinohattan was free from his tyranny and Daisy's father, the old king, was evolved back to normal.
Koopa has a similar personality to that of Bowser in the games at the time. However, he also is shown to have an understandable motive in regards to re-merging both dimensions, citing that he intends to use Daisy to merge them for the future of his species, especially since his species has to go through several hardships that stem from the parallel world being a near-complete wasteland. Despite this, Koopa still sees himself as an evil person; while pretending to be a lawyer for Mario and Luigi, he tells them that he "is one evil, egg-sucking son of a snake," and does not deny this after his true identity is revealed.
Koopa has also been shown to be a germophobe. When he first meets the Mario brothers, he shakes their hands, but wipes his hand off with tissues afterward; after assaulting Luigi soon afterward, a police officer spray his hands with disinfectant, and even later he has a lab technician devolved into primordial ooze simply for sneezing in his presence.
President Koopa is entirely human in appearance, with blonde hair he gels in the shape of a crown, and he frequently wears a black business suit and tie. However, after being briefly exposed to his own Devo machine by the Mario Bros., he started occasionally possessing some reptilian traits, such as a long, pointed tongue, slitted pupils, and in a few instances his entire face briefly morphing to become more reptilian. Near the end of the film, Koopa is forcibly de-evolved into a snarling green Tyrannosaurus Rex, then into a large glob of primordial ooze.