In human form, Reiner has short blond hair, hazel eyes, and a defined facial structure. His large height, broad shoulders, and serious expression give him an intimidating presence. In the year 854, Reiner has slightly longer hair, possesses a short goatee and has lost weight making his cheekbones appear more defined. He has also grown taller. Reiner's Armored Titan form was 15 meters tall and had white plates of hardened skin[14] covering the entirety of its body, except for muscles in its cheeks that become exposed when it opened its lipless jaw, as well as the muscle tissue behind its knees, elbows, and feet. Its eyes were covered by white, organic lenses, and it had short, blond hair. While fighting Eren, it has been noted that it had high agility and was capable of moving at a fast momentum, despite its seemingly-heavy weight and being low on stamina. His Titan was also able to harden its hands and feet which create sharp claws that could be used to climb certain structures, such as the Walls. As a child, Reiner was rather quiet and meek yet at the same time very loyal and driven. He believed that if he became a Warrior then his Marleyan father would come back[16][17] and deluded himself into thinking he would still cheer him on as he fought the Eldians, even after he rejected him.[18] Because of his motivation, Reiner was very desperate to become a Warrior, even going as far as to accuse Galliard of being an Eldian spy when he belittled him. However, after he was chosen to inherit the Armored Titan, Reiner gained a newfound self-confidence, though it was quickly shattered when Marcel revealed that he was not chosen for his abilities. Due to Marley's propaganda and his mother's influence, he believed the Eldians of Paradis Island to be "devils" and that he would become a hero by exterminating them. He was also very gullible, never doubting the words of his mother and superiors. Following Marcel's death, Reiner began incorporating elements from his personality into his own. He became more decisive and assertive, even willing to threaten Annie and Bertolt to ensure they followed his orders, yet also deeply caring and genuinely desiring to protect them. He also accepted that his belief that his father would return if he were to become a Warrior and defeat the Eldians was just a fantasy. In addition to this, Reiner started to develop a negative perception towards himself, believing he was supposed to have failed in becoming a Warrior and that he should have been the one to die instead of Marcel. By the time he joined the 104th Training Corps, Reiner had completely incorporated Marcel's personality into his own. He built up a reputation of being a passionate and honest person with a strong sense of duty who takes his role as a soldier very seriously and encourages others to do the same. However, he was 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 was stated to be the "big brother" of the other trainees. However, beneath this facade, Reiner developed serious emotional and mental problems as a result of living a double-life. While still loyal to his true cause as a Warrior of Marley, he was unable to cope with the guilt he felt towards his actions and thus began to suppress his true memories in an effort to escape. Having to kill Marco seems to have been the final straw for him, causing him to snap and developing psychological issues. During these times, he would forget his actual identity and truly believes himself to be an Eldian soldier. Even after blowing his and Bertolt's cover, he initially still continued to shift between his two personas. However, after Bertolt bluntly told him that he was not a "soldier" but a "warrior", Reiner was, though with some difficulty, able to set his priorities straight. Following the failure of the Paradis Island Operation and fighting in the Marley Mid-East War for four years, Reiner's personality has changed so much that both his mother and cousin noted that he seems like a completely different person.[25] Despite the fact that they are enemies now, Reiner harbors little to no malice towards his former comrades, only sarcastically referring to them as "devils" while humanizing their actions and beliefs before his family.[26] He also suffers from constant nightmares about his near-death experiences and frequently sees memories of his childhood. Eventually, Reiner's negative perception towards himself reached its lowest point and caused him to contemplate committing suicide. However, despite stating that he wants to die, he cannot bring himself to, as his dedication toward his loved ones still exceeds his self-loathing. However, in spite of all his emotional issues, Reiner is very intelligent with notable leadership qualities, able to think clearly, analyze situations, and formulate effective plans.[28] As Eren himself confirmed, he is able to think ahead and in the long term, able to accurately predict the consequences depending on the course of action taken, all while maintaining his composure.[29] He understood the hidden meaning behind Zeke Yeager's words when he indirectly implied that the Warriors' meeting was being bugged by their Marleyan superiors, and acted accordingly, quickly agreeing to his Captain's plan and intentionally cutting off Galliard before he could run his mouth too much. During their mission on Paradis Island, while it was Annie's job to gather the information, it was mostly Reiner who strategized, coming up with efficient multi-step plans not long after acquiring intel from her.[30] As a leader, Reiner is also very devoted to his mission, to the point that he refused to talk and was ready to die when he was the Survey Corps' prisoner and Hange Zoë threatened to kill him for not cooperating. Reiner comes from the Liberio internment zone in Marley, which he refers to as his hometown. He was born to an Eldian mother, Karina Braun and a Marleyan father. Growing up, he was not allowed to see his father, as relations between Marleyans and Eldians were strictly forbidden. As a child, it was decided between him and his mother that he would become a Warrior candidate and potentially inherit one of the Nine Titans so that Reiner and his mother could become honorary Marleyans and reunite with Reiner's father. As a Warrior candidate, Reiner was very weak, his only skill being his strong loyalty to Marley.[34] One day, he learned from another Warrior candidate, Zeke, that in a few years, the operation to reclaim the Founding Titan would begin, and six new Warrior candidates would be chosen to inherit the power of the Titans.[35] He was mocked by Porco Galliard, a prime candidate to inherit the Armored Titan, for this, claiming that he would have to wait thirteen more years to inherit the Armored Titan. This led to a fight that ended when Marcel pulled his brother back and the others left with Zeke.[36] It was during this that he trained with fellow Warrior candidates Annie Leonhart and Bertolt Hoover. Bertolt attempted to convince Reiner to give up his aspirations, as he would only live for thirteen more years. But Reiner believed that after those thirteen years, he would be a hero to the people of Marley and be the best son in the world. Marcel Galliard ultimately influenced the army, leading to Reiner being selected to inherit the Armored Titan in place of his brother Porco. Alongside the other Warriors, the six Titans crushed an entire nation, leading to them being regarded as a stronger group than their predecessors.

Depressed, tired, self loathing, sensitive, conflicted, desperate, caring