He is a red anthromorphicic Carcharodontosaurus that wears armor over his upper body with the Battlesaur crest over his chest and armor that covers his lower body that looks similar to Greek armor. He often carries a mace with red plastic crystals protruding out the round center.
He is shown to have romantic feelings for Trixie, immediately being intrigued with her and saying she was different than the females he was accustomed to (which is most likely a compliment as the females are shown to be unusual). He tends to speak Shakespearean (even after he discovers he is a toy) and is initially deluded (not knowing he is a toy and believing he is a Battlesaur and that battle was everything wihch Buzz ironically found unbelievable). Despite this, he was shown to be friendlier to Trixie and the gang in contrast to his fellow "warriors" as he welcomed Trixie and Rex as they were dinosaurs like the rest of his tribe (though he ignored the rest of the gang and even proceeded to beat them during the Arena of Woe). He was particularly taken with Trixie and complimented her often while also being intrigued by her views of the world and the type of world she lived in. However, he was also initially loyal to his way of life as he turned on Trixie and Rex after learning they had "the mark of submission" (Bonnie's name written on her hand) and since Battlesaurs never surrender, he believed she was a traitor and allowed her gang to be captured while he proceeded to chase after her to prevent her from getting Mason and Bonnie to help. This shows he resents those who feel betray him as he became bitter after the discovery and did not hesitate to chase her to punish her for her "submission and betrayal". While he chased her, he began to realize the truth of his existence but took some time to accept it. It was ultimately his confrontation with Trixie as she was about to shut off the video game Mason and Bonnie were playing that led him to realize he was a toy and his true purpose wasn't battle but to be a toy and to surrender himself to his owner "Mason" and play. He has since reconciled with Trixie and awaits the next time they meet.
After Woody, Buzz Lightyear, Trixie, Rex and Angel Kitty enter the Battlesaur playset, Reptuillus Maximus welcomes Rex and Trixie in their quality of being dinosaurs, while completly ignoring the three other toys. He starts to fall for Trixie, who he finds "quite unlike our females," and makes her visit all the parts of "Battlepolis." However, he does not understand Trixie when she talks about toys and play, stating that he would not accept to "surrender."
Reptillus shows off his gladiatorial prowess in the Arena of Woe by "slaughtering" the toys captured by the Battlesaurs. He is puzzled, however, when Trixie attemps to stop him. In the process, he discovers that Trixie has the name of Bonnie under her foot, which he and the Battlesaurs consider to be a sign of surrender. Reptillus feels deceived by Trixie and expresses bitter disappointment of her.
He chases Trixie when she flees to bring in Bonnie and Mason and gets out of the Battlesaur playset. In the process, he stumbles upon his own box. He is horrified by this finding, but refuses to face his reality and knocks down the box. He prevents Trixie from turning off the power of Mason's video game console and confronts her. Trixie convinces Reptillus of the greatness of being a toy. Reptillus finally accepts to surrender and lets himself be picked up by Mason and be played with. He is transformed by the experience. During the credits, he expresses his hope to see Trixie again.
- "Who goes there?"
- "What fearsome dinosaurs are these?"
- "Greetings. I am Reptillus Maximus!"
- To Trixie: "You're… not like our females."
- "Are dinosaurs not welcome in our great city, wise cleric?"
- "To the armory!"
- "Raygon, indulge this dinosaur goddess [Trixie] in your finest wear!"
- (Trixie: Have I mentioned what a wonderful time I'm having?") "It is as plain as the horn on your face."
- To Rex: "I haven't forgotten you brother!"
- To Trixie: "The elders shall gaze upon this Battlesaur with full and rapturous pride."
- "Come. Battleopolois awaits!"
- "That was... glorious."
- "Farewell, Trixie of the Bonnie Tribe. My heart will burn bright with the moment of your return. Tuesday, around 3:30."
- Buzz is ironically surprised that Reptillus and the other Battlesaur toys do not know they are toys, despite the fact he was also initially deluded like them as he thought he was an actual space ranger. However, it took Reptillius less time to realize he was a toy than Buzz and it was the entire tribe of Battlesaur toys that weren't aware of this fact since they were never played with and were tricked by the Cleric.
- By the events of the film, he has the name Mason written on his hand, similar to how Trixie has the name Bonnie written on her foot.
- The Battlesaur crest over his chest on his armor beeps and glows red when pressed on.