Bertholdt Hoover, an Eldian raised in Liberio's internment zone on the Marleyan continent, entered the Marleyan military's Warrior candidate program as a child. There, he witnessed Porco Galliard bullying Reiner Braun; after aiding Reiner, they forged a lifelong bond. Selected alongside Reiner, Annie Leonhart, and Marcel Galliard to inherit Titan powers, Bertholdt acquired the Colossal Titan, demonstrating immediate proficiency. In 845, he joined the mission to infiltrate Paradis Island and reclaim the Founding Titan. Approaching Wall Maria, the Warriors encountered Ymir's mindless Titan. Marcel sacrificed himself to save Reiner while Bertholdt reportedly fled in terror. Reiner later persuaded the reluctant group to continue. At Shiganshina District, Bertholdt transformed into the Colossal Titan, breaching Wall Maria’s outer gate. This allowed Titans to invade, causing mass destruction and deaths—including Carla Jaeger. Posing as refugees from a destroyed mountain village south of Wall Maria, a cover story taken from a deceased soldier, Bertholdt, Reiner, and Annie spent two years working odd jobs while gathering intelligence before enlisting. Physically, Bertholdt stood 192 cm (6'3") and weighed 81 kg (179 lbs), making him the tallest known human. He had short black hair, pale green eyes (sometimes noted as brown), thin eyebrows, and an elongated face, often exhibiting nervous sweating. In the 104th Cadet Corps, he wore the standard trainee uniform; later, as a Scout, he adopted their gear, including a green hood during missions. Casually, he favored a blue sweater over a white button-down shirt with tan pants. His Colossal Titan form reached 60 meters, towering over most Titans. This form lacked skin, exposing muscle tissue, and constantly emitted steam—mirroring his human sweating. Its facial structure bore little resemblance to Bertholdt’s human features, with disproportionately long, slender arms, swollen pillar-like feet, and no sexual organs. Quiet, withdrawn, and taciturn, Bertholdt typically lingered in the background, self-described as weak-willed and a follower. His Cadet Corps instructor, Keith Shadis, noted his potential but criticized his lack of initiative. Bertholdt admitted to cowardice and struggled with low self-esteem. Yet he harbored fierce devotion to fellow warriors Reiner Braun and Annie Leonhart, reacting intensely when either was threatened. Though initially seeming the least affected by their actions against humanity within the Walls, the Battle of Trost District revealed profound inner conflict and guilt, particularly over comrade Marco Bott’s death, which reduced him to visible distress and tears. He held unspoken feelings for Annie and showed kindness, such as in interactions with Ymir. Pragmatism surfaced when he cautioned Reiner about maintaining their cover. In the 104th Cadet Corps, Bertholdt excelled with vertical maneuvering equipment. During training, he and Reiner assisted Eren Jaeger after faulty gear struggles, warming to him upon learning they shared a goal to reclaim their homeland. Bertholdt graduated ranked 3rd. Though aspiring to join the Military Police Brigade for safety, he felt conflicted after witnessing Eren’s resolve to enlist in the Scouts. Ultimately, he, Reiner, and Annie planned to join the Military Police to access the interior. Five years post-Wall Maria’s fall, in 850, Bertholdt transformed again at Trost District, breaching the gate. He destroyed the Wall’s artillery with an arm sweep and repelled trainees with scorching steam. After observing Eren preparing to attack—an act he initially dismissed—he witnessed Eren emerge from his Titan form protecting Armin Arlert, leading to Eren’s capture and trial. During the ensuing custody conflict, Bertholdt and Reiner’s identities as the Armored and Colossal Titans were exposed when they kidnapped Eren and Ymir, fleeing toward Wall Rose.