About Dinosaur Ryuzaki
Dinosaur Ryuzaki plays a deck focusing on Dinosaur-Type monsters, although his mightiest monsters are Dragon-Type. He is the runner up in the regional championship, losing the final round to Insector Haga. He is not a cheater like Haga, but is a jerk all the same.
In the manga, Ryuzaki is portrayed as rude, brash and dis-likable but not villainous: in his second appearance, he displays no more hostility towards the protagonists that usual. He is also displayed as a genuinely skilled and dangerous duelist, whose defeats usually demonstrates that the other duelist means business.
However, the last seasons of the anime adaptation portrays him as a joke easily dispatched by the villains, and willing to sell his soul to get revenge on Joey. They also portrays him as Weevil's best friend and partner in crime, something much less apparent in the manga.
Ryuzaki entered Duelist Kingdom, Pegasus' tournament. On the boat, he made it clear that he thought rules were for wimps. He fell in love with Mai Kujaku, who dueled him, in which if she won, she would get his room, and if he won, she'd give him a kiss. Mai won and kicked Ryuzaki out of his room.
Ryuzaki later attempted to duel her again as revenge, and she decided that she would if he could defeat Katsuya Jonouchi in a duel. Ryuzaki challenged Jonouchi to a duel in which his friends were forbidden from helping him. Jonouchi accepted, and soon faced the wrath of Ryuzaki's most powerful monster, the Red Eyes Black Dragon. He eventually made a bet with Jonouchi, staking their rarest cards (Ryuzaki's Red Eyes vs. Jonouchi's Time Wizard) on the outcome. Jonouchi defeated him using Time Wizard, taking his Star Chips and Red Eyes, and Ryuzaki was eliminated from the tournament.
Ryuzaki entered Battle City, but was eliminated when Esper Roba, a duelist who claims to have psychic powers (but in reality has his brothers tell him what cards are in his opponents' hands), defeated him. He then stayed around to see the outcome of Esper's duel with Jonouchi, while scolding the latter.
Waking the Dragons
In Season 4, Waking the Dragons, Haga and Ryuzaki attempted to steal Yugi and Jonouchi's rare cards, but were challenged to a duel by Grerimo, who beat them and took their souls. They were released after Yugi defeated Grerimo. Haga and Ryuzaki snuck aboard during Yugi's trip over to Pegasus' castle in the hopes of finding rare cards, and tried to get an Orichalcos card from Rafael, and became two of Dartz's henchmen after hitchhiking aboard Rafael's helicopter. Rex dueled Jonouchi in a train station as revenge for taking his Red Eyes, and was defeated. His soul was taken by the Orichalcos, and was released when Dartz and the Orichalcos God were defeated.
In the first half of Season 5, Grand Championship, Hag and Ryuzaki entered Kaiba's tournament as one duelist, and dueled Siegfried von Schroider, who easily defeated them with his Valkyries.
Dawn of the Duel
In the second half of Season 5, Dawn of the Duel, Haga and Ryuzaki stole Yugi's Millennium Items and Egyptian God Cards (only going after the latter), but ran into Yami Bakura, who temporarily trapped their souls in the Shadow Realm and returned the cards and items to Yugi. They suffered a lot of the consequences of Zorc ravaging the past, but survived it all.