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Tyranno Hassleberry, known as Kenzan Tyranno (ティラノ剣山 Tirano Kenzan?) in the original Japanese language version, is a fictional character in the Yu-Gi-Oh! GX anime series. In the English version, Tyranno is voiced by David Wills, while Hiroshi Shimozaki takes the role in the Japanese version. In both versions, people tend to call him only by his last name.
A physically-built duelist with a very muscular physique who draws his strength from a mysterious source, Tyranno is introduced during the second season as one of Jaden Yuki's new allies.
In the timeline of the Yu-Gi-Oh! GX anime, while participating in an archaeological dig, Tyranno was hospitalized after a rock slide permanently damaged the tibia of his left leg. The bone fragment of a dinosaur fossil he unearthed during the excavation was used to replace it, and as a result, a great power awoke within him due to his dinosaur DNA contained within the bone It is implied that this accident is the reason for Tyranno's unique ability to narrow his pupils into reptile-like slits and is also supposedly what would later protect him from being converted by Sartorius into one of the members of the Society of Light.
Tyranno enters Duel Academy in the second year. To his surprise, he was assigned to the Ra Yellow dormitory despite scoring high on the entry exam because he did not attend an associated preparatory school, which would have granted him access to Obelisk Blue. Heading a gang and stealing the Duel Disks of those he defeats, he quickly meets and challenges Jaden Yuki to a Duel, but was defeated and returned the stolen items, quickly coming to idolize Jaden. Although his dormitory is technically Ra Yellow, he decides to live in Slifer Red to be closer to and learn from Jaden. From his introduction onwards, he often fights with Syrus Truesdale over who is better suited to being Jaden's best friend (in the Japanese version, it is over who has the right to call him "big brother").
At the end of the second year, Tyranno, along with Linda, chase after Prince Ojin as he prepares to arm the mind control satellite of Misgarth. Unleashing the full force of his dinosaur DNA power and assuming a Duel Spirit form (which is a brown Tyrannosaurus rex, hence his name "Tyranno"), he travels into space with Elemental Hero Glow Neos to divert its blasts. While the returning Sarina keeps it from firing any further, the two are successful in destroying the satellite.
With the start of the third year, Tyranno chooses to remain in Ra Yellow instead of advancing to Obelisk Blue; to him, the issue of which dormitory he is officially a part of is irrelevant. Agreeing to aid Jim Crocodile Cook in his investigation of mysterious electromagnetic waves coming from the jungle, his dinosaur DNA reacts to additional signals sent by Professor Viper, which render him uncontrollable. Jim duels with Tyranno in a Survival Duel and successfully reverts him to his former self within the first few rounds of the battle, ultimately claiming victory. He is later the last of 4 sacrifices used for the completion of the Super Polymerization Card, but returns, however, after the duel between Jaden and Yubel.
In season four Hassleberry is still in his second year, which means he won't graduate this year. He enters the tag team tournament with Blair and duels Jaden and Alexis. Later on in the year, Tyranno runs into his friend, and fellow second-year, Sorano; however, he is under the control of Trueman and duels Tyranno, but unfortunately fails and is the first main character consumed by the darkness, joining other students. He later is saved as the other students by Jaden. His last message to Jaden was to not forget him.
In the English version, Tyranno speaks with a Southern accent, and uses stereotypical cowboy slang and military jargon (leading Jaden and Syrus to call him Sarge), while his original series counterpart does not do this, and instead ends the majority of his sentences with either "(da) don" (Japanese explosion onomatopoeia) or "zaurus" (the Japanese equivalent of "saurus").
Tyranno plays a Dinosaur deck, relying on summoning high-level monsters quickly, such as Black Tyranno and Ultimate Tyranno. Tyranno does so using a various assortment of cards, including New Ultra Evolution and Ultra Evolution. Several of his cards allow him to take advantage of his opponents placing their monsters in defense position, including Black Tyranno along with Dark Driceratops.