Claude Duvalier is an instructor of the Training Corps and a former member of the Survey Corps. He is the author of the "white paper," an unofficial collection of military information and tactics intended for the education of new trainees.
Claude is a courageous man proudly devoted to the cause of the Survey Corps. He believes that the most important thing is to kill the Titans, and detests the corruption and arbitrary displays of power of the Military Police Brigade and other authorities. He is not afraid to speak his mind against these practices even if that means his own death.
At some unknown point in time, Claude joined the Survey Corps, and presumably spent a long period among their ranks as he gained a vast experience in the tactics, structure and history not only of the Corps but the military in general. After his retirement, he became an instructor of the Training Corps.
Personality: Claude is a courageous man proudly devoted to the cause of the Survey Corps. He believes that the most important thing is to kill the Titans, and detests the corruption and arbitrary displays of power of the Military Police Brigade and other authorities.
History: At some unknown point in time, Claude joined the Survey Corps, and presumably spent a long period among their ranks as he gained a vast experience in the tactics, structure and history not only of the Corps but the military in general. After his retirement, he became an instructor of the Training Corps.
Claude Duvalier in the story: Some time after the fall of Wall Maria and the failed plan to reclaim the Wall, and seeing that the military has lost many good soldiers and has barely any resources left, Claude decides to write a "white paper" detailing what he learned through his battles against the Titans, with the purpose of encouraging trainees to join the Survey Corps. He writes the document on his own accord, stating that it does not reflect the official stance of the Corps, and instructing the reader to burn it afterward.
Abilities: Claude possesses a considerable knowledge of the tactics, structure and various aspects of the history of the three divisions of the military. He is considered skilled and experienced enough to be appointed as instructor of the Training Corps.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.