Reiner Braun (ライナー・ブラウン) is a passionate person, with a strong sense of duty. He takes his role as a soldier very seriously, and encourages others to do the same. However, he is also noted to have a kind heart and a tendency to always think of others before himself, taking on extra burdens for the sake of his comrades. He is stated to be the "big brother" of the other trainees. However, he is also revealed to have serious emotional and mental problems as a result of his actions. While still loyal to his cause, he was unable to cope with the guilt and has begun to suppress his true memories in an effort to escape.
During his time training to become a soldier, he was considered to be one of the most adept with the 3D Maneuver Gear. Reiner graduated 2nd in his class. As one of the top ten graduates of the 104th squad, Reiner is likely highly competent in the use of 3D Maneuver Gear and respective weapons. He is also one of the best hand-to-hand fighters amongst the recruits.