Isidore Rhodes, known in the original Japanese version as Fubuki Tenjouin, is a student at Duel Academy and a senior member of the prestigious Obelisk Blue dormitory. He is the older brother of Alexis Rhodes and was once considered one of the most talented and popular students at the academy, earning the nickname the Blizzard Prince for both his dueling skills and his charming, star-like persona. However, before the start of the series, he mysteriously vanished from the campus, an event that deeply troubled his sister and friends and set the stage for his troubled return.

Isidore possesses a naturally cheerful, dramatic, and good-natured personality. He is energetic, charismatic, and often acts in a flamboyant manner, reflecting his love of the spotlight and showmanship. Before his disappearance, he was known for his confident and friendly demeanor. However, this persona is contrasted sharply by a darker and more serious side. When he is reintroduced, he is under the control of the entity known as Darkness, having been possessed by the Shadow Charm known as the Mask of Darkness. In this corrupted state, he is cold, ruthless, and speaks with a menacing tone, serving as one of the Seven Shadow Riders. After being freed from this influence, his original personality resurfaces, and he becomes a supportive and reliable ally, though he sometimes struggles with the guilt and trauma of his actions while possessed.

His primary motivation throughout the series is to protect his friends and family, particularly his sister Alexis, and to atone for the pain he caused while under Darkness's control. His mysterious disappearance was the result of being lured to the abandoned Obelisk Blue dormitory, where he fell victim to Darkness and was forced to become a servant. After being defeated and saved from the mask by Jaden Yuki, Isidore is driven by a desire to reclaim his life and make amends. In later seasons, he also becomes deeply invested in confronting the lingering threat of Darkness permanently and in recovering lost memories of his past, including a close friendship with a student named Yusuke Fujiwara.

In the story, Isidore fills the important role of a former antagonist who becomes a key supporting character. He appears in season one as the masked Shadow Rider, a powerful opponent who tests Jaden early on. After his rescue, he rejoins Duel Academy as a senior student. In season two, he is one of the few Obelisk Blue members who resists the influence of the Society of Light, remaining loyal to his friends. He notably gives Jaden a crucial card that helps break Sartorius's control over Alexis. In season three, he volunteers to accompany Jaden into another dimension to search for a lost friend, demonstrating his courage and loyalty. He is temporarily sacrificed during a duel against a powerful enemy but is later revived. Throughout season four, he confronts the ultimate return of Darkness, seeking answers about his past and facing his former friend Fujiwara in a final, emotional duel.

His most significant relationship is with his sister, Alexis Rhodes. He is very protective of her and acts as a caring, if sometimes overbearing, older brother. Their bond is a central part of his character, and his disappearance had a profound effect on her. He also shares a close rivalrous friendship with Zane Truesdale, who was his equal in dueling skill during their time as top students. He looks up to Jaden Yuki out of gratitude for saving him and respects his dueling abilities. He also had a deep friendship with the student Yusuke Fujiwara, whose own fall into darkness is directly connected to Isidore's past.

Isidore undergoes significant development, transitioning from a helpless victim and unwitting villain to a remorseful hero. His arc involves confronting his past weaknesses and the darkness within his own heart, ultimately striving to be a force for good and to protect the academy he once inadvertently helped endanger.

Regarding his notable abilities, Isidore is considered a top-tier duelist, ranked among the best at Duel Academy, second only to Zane Truesdale in his prime. In the anime, he is most famous for using a Red-Eyes Deck, centered around the powerful Red-Eyes Black Dragon. While under the influence of Darkness, he wields a corrupted version of this deck that includes monsters like Red-Eyes Darkness Dragon. When not in serious combat, he has also been shown using an Idol Deck, which is themed around entertainment and stage performance, reflecting his love for stardom and showmanship. In the manga adaptation, he uses a Sphere Deck, which focuses on a unique strategy of equipping his monsters to the opponent's field to gain advantages.