Rex Raptor, known as Dinosaur Ryuzaki, in the manga and Japanese anime, is a "Dinosaur" Duelist. Despite his introduction as a powerful Duelist, he becomes a source of humiliation along with his companion Weevil Underwood after suffering defeat to Joey Wheeler, and begins considering Joey his rival for this reason. Though Rex is vengeful, arrogant, and tyrannical, he plays fairly.
"Dinosaur" is a nickname; "Ryuzaki" is his given name. In the English anime, he is named after the Tyrannosaurus Rex and the Velociraptor, 2 types of dinosaurs.
In the Japanese anime, Ryuzaki speaks with a Yokohama accent.
Rex's character design was overseen by Kazuki Takahashi. His usual outfit consists of a green jacket and a red beanie cap, plus tan pants. In duelist kingdom, he wears a tan vest-thing on his jacket, and a black shirt. In Battle City onward, he wears a green jacket, and a yellow shirt. His hair is brown with dyed purple strands next to his forehead. He has purple-blue eyes, whenever his irises are shown (his pupils are usually too small to determine his eye color). He carries a KaibaCorpDuel Disk on his left hand. In the Waking the Dragons arc he has a Chaos Duel Disk.
In the first Toei Animation movie, Ryuzaki has black hair with dyed pink strands and a purple cap.
Rex was invited to the Duelist Kingdom tournament. Being a runner-up, in the last tournament, he was one of the few participants given a room on the boat journey. He invited Mai Valentine to his room. Mai challenged him to a Duel, where she would give him a kiss if he won (do anything he wants for him the Japanese Version), but she would get the room to herself if she wins.
Confident that he wouldn't lose, Rex accepts. However Mai insisted that they use her cards. Unbeknownst to Rex, Mai sprayed them with different perfumes and was able to tell what cards he drew. With this advantage, Mai won and booted Rex out of the room.
During the tournament, he was constantly berated by the fact Mai had more Star Chips than him. He challenged her to a Duel to get revenge but Mai, preferring to avoid him, was content to use the excuse that she had already "beaten" him once. However since Mai had previously lost to Joey Wheeler and considered it obnoxious to challenge him again, she agreed to duel Rex, if he defeated Joey for her.
During his Duel with Joey, Rex gambled "Red-Eyes Black Dragon" in the hopes of winning Joey's "Time Wizard". (In the anime, "Red-Eyes Black Dragon" was an incredibly rare card that Rex received as a prize for being a runner-up in the last tournament.) This infuriated Mai as it would mean, Rex's Deck would be even stronger if she had to face him. However, Joey won the Duel and claims Rex's "Red-Eyes".
In the Waking the Dragons arc, it was revealed that he and Weevil lost a good deal of their popularity after the tournament and they eventually ended up wandering Domino City where they were ambushed by Gurimo. Their souls were taken, and later released when Yugi Muto defeated him.
The two of them then trailed after the party until Yugi's soul was taken by Rafael and they begged him to take them on their Helicopter. Rafael and Alister took them to Dartz, who agreed to give them power if they passed the necessary test. Each of them was given a piece of the Orichalcos Stone and both must succeed in grasping them, which both of them did.
Rex and Weevil improved their Decks by taking cards from Dartz's massive collection and Rex challenged Joey to a rematch. During the duel, Joey used Rex's "Red-Eyes Black Dragon" against him, much to Rex's displeasure and anger. Despite using "The Seal of Orichalcos" Rex lost at the hands of Joey's "Gearfried the Swordmaster," sending his soul to Dartz again. He was released at the end of the arc when Dartz was defeated. He and Weevil fled from the hospital they found themselves in.
Sebastian Arcelus replaces Sam Regal as Rex's voice for this season; Rex's voice is higher pitched than it was in seasons 1 and 2.
Rex and Weevil's last attempt at revenge was to steal Yugi's Egyptian God Cards from his house, where they mistakenly grabbed Yugi's bag containing all of his Millennium Items. Yugi tried to stop them, but couldn't catch up. While examining their prize, they were then attacked by Yami Bakura, who stole the Millennium Ring back from them.
Ryuzaki is shown in the last episode of Yu-Gi-Oh! dueling with Haga (not seen in the U.S.).