Adrien Gecko

Adrian is the eldest son of the Gecko Family, which has considerable influence over the world's petroleum, heavy chemical industry, and information technology. Abandoned by his parents when he was young, Adrian developed an inferiority complex that convinced him that he had nothing left to live for. He observed the sky and awaited death but was one day adopted by the Gecko Family which intended for him to become its heir in light of the family's failure to produce a biological child to fill the position. However, when a son named Shido was finally conceived, Adrian grew jealous of his younger brother (in the Japanese version, he contemplates killing him), but chose to continue working diligently for his sibling's sake. In the dub, it states that he completely forgot about his vendetta during the timeskip.

From the outset of the third year Adrian works undercover to learn more about Viper's plot and secretly acquire Yubel's power for himself, being aware he was affiliated with the spirit. Eventually, he is approached by Thelonious Viper himself, who threatens to return him to East Academy if he refuses to Duel in a Survival Duel. Suspecting that he will set the Bio-Band energy absorption level on maximum—which can cause death—for his scheduled Duel, Adrian invites students to a party to participate in Survival Duels with one another, intending to overload Viper's project. As he leaves the Obelisk Blue dormitory, however, Chazz Princeton lifts him off the ground by helicopter, challenging him to a Duel. Intrigued by Chazz's determination stemming from his time at North Academy, Adrian reveals the hellish past that he too has suffered. Despite this similarity, he concludes that Chazz is "nothing special", and that although he wins the Duel, the energy absorption level on his Bio-Bands was not minimized enough to prevent him from collapsing.

Adrian presents himself as somewhat of a party animal, and is witty to the point where he sometimes pokes fun at the series itself, such as in episode 112. Adrian appears to be extremely loyal to his family despite his personal views as shown when he saved his brother from death even though he would become the heir to the company. Adrian speaks with a youthful, yet monotone voice. For some reason, he never uses any contractions, which gives him an almost robotic quality.

Adrian is a swarthy-skinned, extremely muscular young man. He has magenta hair that stands up in wavy spikes, and eyes described by Kazuki Takahashi as kind and soft. Adrian wears large ovular spectacles, and his ears are pierced with black studs. He wears a necklace of large black beads with a blue tassel. Adrian wears a sleeveless brown jacket with an Academy-style clasp, an orange sash, tan pants, and black shoes and socks that cover his pants up to the knees.