Mortu is a compassionate, loyal and patient Utrom. Like all Utroms he is gifted with an extraordinarily long lifespan and therefore is willing to wait for an opportunity to leave Earth. His primary motivation is to protect his race and get them away from Earth safely. Despite this, he also shows a great deal of loyalty to anyone whom he considers a friend, whether they are an Utrom or not. While the Utrom's safety is his first priority, he will also do anything he can to help people he cares about, going out of his way to free the turtles from their stasis pods and forming a close friendship with Splinter after healing him from the injuries he received in his battle with the Shredder. Possessing an intelligent and peaceful mind, Mortu is devoted to peace but can fight when the situation calls for it, being able to hold his own against the evil Ch'rell in combat. Mortu and Ch'rell have a deep loathing for each other and while Ch'rell wants revenge on all the Utroms, Mortu is the one he seems to hate the most, no doubt due to him being the Captain of the ship the Utroms used to imprison him. Despite his peaceful personality, Mortu shows that some of his thought processes are on a similar wavelength to Raphael, as shown when he said "Big talk, little slime ball" to Ch'rell which Raph had said only seconds ago whilst Mortu could neither see nor hear him.
Mortu was the captain of a spaceship that was transporting the dangerous criminal Ch'rell to prison. Unfortunately, Ch'rell managed to escape and crash-landed the ship on Earth, arriving in 11th century Japan. Despite the fact that the current level of technology on Earth was insufficient to repair their ship, Mortu was confident that Earth will one day have what they need. To hide amongst the humans, the Utroms constructed exo-suits with proper coverage to disguise themselves as humans. They met a number of warrior humans, whom they trusted and made them Guardians. However, Ch'rell had also had survived and hijacked the prototype exo-suit and covered it with samurai armor, taking on the guise of the Shredder, whom they would secretly battle for a millennia.
In the 20th century, when Mortu was attacked by Foot Ninja, he was saved by Hamato Yoshi and Yukio Mashimi but his exo arm revealed his true nature to them and he offered them a chance to join the Guardians, which they did. But Mashimi betrayed them to the Shredder when he constantly failed to succeed in advancement. But the Utroms escaped to New York, where they set up T.C.R.I., a company to hid their transmat. In his human guise, Mortu was the CEO for the official statements.
However, the Turtles were looking for a missing Splinter, who disappeared after the battle against the Shredder, found him in the TCRI building. But security accidentally brought them to the transmat, which sent them across the galaxy. Mortu was able to get them back, bringing along the Fugitoid and soldiers from the Triceraton Republic and the Federation. Mortu tried to mediate things but the two groups were obsessed with capturing the Fugitoid, forcing them to be put in stasis and sent back to their original location. Mortu then showed the Turtles and Splinter the history of the Utroms through use of the oracle pods. But Baxter Stockman sabotaged the pods, trapping them inside the virtual environment. Luckily, the virtual Mortu inside provided them with a fail safe. Then the Shredder and the foot Clan invade the compound, intending to use the transmat to conquer the Utrom homeworld. Thanks to Honeycutt, the Shredder's control over Stockman was useless and rendered his "master" unconscious. But the Shredder dropped an implosion device that threatened the building, forcing the Utroms to evacuate home through the transmat. Mortu offered Honeycutt asylum on their homeworld, which he accepts.
Mortu later returned to Earth to recapture Ch'rell, finding that he had constructed a ship to conquer their homeworld. As the ship's core was overloading, Mortu ordered a stasis field put around it and everyone transmatted off it. He brought all personnel on the ship back to the Utrom homeworld, where Ch'rell stood trial.
Mortu is one of those in attendance to witness Casey and April's wedding vows in Wedding Bells and Bytes. Also, his men had made sure that there was no sushi bar, as the last time Mortu resulted in smelling like soy sauce (this is likely due to the Utroms' body texture being similar to many cuts of sushi).
- The name, Mortu, is simply "Utrom" backwards.