Bertholdt Hoover was an Eldian born in Liberio's internment zone under Marleyan rule. Enrolled as a child in Marley's Warrior program, he witnessed Porco Galliard bullying Reiner Braun. After aiding Reiner, the two forged a lasting friendship. Bertholdt was chosen to inherit the Colossal Titan, a sixty-meter Titan capable of releasing intense steam and causing massive destruction through explosive transformations; he mastered this power almost instantly. In 845, alongside Reiner Braun, Annie Leonhart, and Marcel Galliard, he infiltrated Paradis Island on a mission to retrieve the Founding Titan for Marley. During this mission, Marcel sacrificed himself to save Reiner from Ymir's Pure Titan, an event where Bertholdt reportedly fled in terror before regrouping. Despite Annie's objections and Reiner's insistence on continuing, Bertholdt breached Wall Maria at Shiganshina District as the Colossal Titan, kicking open the outer gate and enabling a Titan invasion. This act caused widespread death and destruction, including the annihilation of Eren Yeager's hometown and the death of his mother. Following the attack, Bertholdt, Reiner, and Annie posed as refugees from a village south of Wall Maria, forging records and blending into the population for two years while gathering intelligence. Bertholdt later enlisted in the 104th Cadet Corps, graduating third in his class. Instructor Keith Shadis noted his great potential but criticized his lack of initiative, describing him as quiet, weak-willed, and prone to following others, particularly Reiner. Eren Yeager observed his taciturn nature and tendency to remain in the background. During training, Bertholdt assisted Eren with faulty vertical maneuvering gear and formed bonds with fellow cadets like Marco Bodt. Despite these connections, he maintained loyalty to Marley's mission. Five years after breaching Wall Maria, he repeated his actions as the Colossal Titan at Trost District, breaching Wall Rose. His identity was exposed when Reiner revealed their true origins as Warriors during a mission atop Wall Rose. Bertholdt assisted in capturing Eren Yeager and Ymir, though the Survey Corps eventually rescued Eren. Bertholdt, Reiner, and Ymir escaped to Marley territory. Internally conflicted, Bertholdt initially appeared detached but harbored deep guilt over betraying his friends, particularly during Marco's death, where he displayed visible panic and tears. He expressed genuine care for Reiner and Annie, with implied romantic feelings toward the latter. However, during the Battle of Shiganshina, he underwent a significant shift, becoming cold and resolute. He rejected Armin Arlert's negotiation attempts, declaring his intent to kill everyone within the Walls to complete his mission. He rationalized his actions by accepting the world's inherent cruelty, believing no one was solely at fault for the cycle of violence. Transforming near Survey Corps forces, he killed many soldiers instantly with his steam. Armin devised a distraction, resulting in Bertholdt being ripped from his Titan nape by Eren. Severely burned but alive, Bertholdt was fed to Armin, who inherited the Colossal Titan. In his final moments, terrified of Pure Titans, Bertholdt begged for help before being devoured. His death transferred the Colossal Titan's power to Armin, altering the conflict's course.