Bertolt Hoover is a central character in the series 'Shingeki no Kyojin' (Attack on Titan). He is known for his ability to transform into the Colossal Titan, a towering behemoth capable of immense destruction. Initially introduced as a member of the 104th Training Corps, Bertolt is later revealed to be a covert warrior sent by Marley to infiltrate and sabotage humanity's efforts. His character is marked by internal conflict, loyalty to his mission, and the pressure of living with the consequences of his actions. Bertolt's transformation into the Colossal Titan often serves as a pivotal turning point in the series, impacting the storyline and other characters significantly.