Reiner is a member of the Marleyan military's Warrior Unit and is the holder of the Armored Titan (鎧の巨人, Yoroi no Kyojin). As the leader of the infiltration unit responsible for Marley's opening offensive against the Walls in the island of Paradis, he serves as one of the main antagonists for most of the story. Reiner is introduced as a cadet of the 104th Training Corps who graduates 2nd in his class. Described by instructor Keith Shadis as being strong as an ox and a natural leader, he quickly earns the trust of the Paradisian Survey Corps and infiltrates their ranks. As a child, Reiner joined Marley's Warrior Unit so he and his Eldian mother could become honorary Marleyans and be reunited with his Marleyan father. Despite being rejected by his birth father, the fanatical patriotism instilled in him by his mother motivates him to move forward with his mission to capture the Founding Titan (aka: the "Coordinate") from Paradis Island.[ch. 95] When the group leader, Marcel, is unexpectedly eaten during their journey, Reiner assumes command over the remaining two Warriors, Annie and Bertolt. They flood Shiganshina with rampaging, 'Pure Titans' by destroying the outer gate of the District then breaking through the gate at Wall Maria. They then disguise themselves as refugees and join the masses of people within Wall Rose before joining the Paradisian military. Unable to pinpoint the Coordinate's location, Reiner orchestrates an attack on Wall Rose to root out its holder. Upon witnessing Eren transform into a titan during the ensuing battle of Trost, Reiner suspects him of possessing the Coordinate and tasks Annie with his capture. However, the plan ultimately ends in failure and Annie is taken captive.

Annie Leonhart is a graduate of the 104th Training Corps and former member of the Military Police Brigade. Her exceptional skills with swords and unarmed combat earned her the 4th rank, but she is also noted to be a lone wolf who struggles to work with others. She possessed the ability to transform into a Titan known as the Female Titan. Trained from an early age by her father, she is selected as one of Marley's Warriors. In the year 845, she is sent on a mission to retrieve the Founding Titan, along with fellow Warriors Reiner Braun, Bertolt Hoover, and Marcel Galliard. As the Female Titan, she serves as a major antagonist prior to her defeat, at which point she crystallizes herself and is left in a comatose state. She was held underground in the custody of the Survey Corps for approximately four years before escaping during a battle between the Military, the Yeagerists, and the forces of Marley.

Bertolt Hoover was an Eldian and one of Marley's Warriors. He possessed the ability to transform into a Titan known as the Colossus Titan. In the year 845, he, Reiner Braun, and Annie Leonhart breached Wall Maria in an attempt to lure out and acquire the Founding Titan for Marley. After that, he joined the military and graduated the 104th Training Corps, ranked 3rd, and later joined the Survey Corps, until his identity as the Colossus Titan was revealed. He was described by others to be a weak-willed and quiet person. His withdrawn behavior initially led to the impression of him being the least emotionally compromised of the three Titan warriors. He showed little attachment or remorse over his actions, seeming to care only about his partner, Reiner Braun. However, when confronted by his former comrades and questioned about their friendship, he revealed himself to be far more conflicted and guilt-ridden than it originally appeared.

Connie hails from the Ragako District of Wall Rose. He sports a buzz cut and has an outgoing and upbeat personality, always trying his best to keep his teammates pumped up and not shying away from encounters with Titans. His training instructor describes him as having a good sense of balance and performs well with the vertical maneuvering equipment, but that he also has a slow mind and makes strategic mistakes. Having ranked eighth in his class, he initially plans to join the Military Police but changes his mind after hearing Eren's speech, and eventually joins the Survey Corps. Later, his village is decimated by the Beast Titan and all of its inhabitants are turned into Pure Titans. Connie is voiced by Hiro Shimono in the Japanese dub of the anime. In the Funimation dub, his name is spelled Conny Springer and he is voiced by Clifford Chapin.

Sasha is a hunter from the mountainous Dauper District. She is tall and lean, and her auburn hair is styled in a ponytail. She is noted as a proficient hunter skilled with a bow and has remarkable hearing and instincts, but she also has issues with structure and authority. She seems obsessed with food and was nicknamed "Potato Girl" (芋女, Imo Onna) for eating one during a military training drill. She joins the military after getting into an argument with her father when he tells her they must give up their traditional hunting lifestyle in the forest in favor of farming to support the large number of refugees moving to the area after the fall of Wall Maria. She manages to become a member of Captain Levi's Elite Squad with a number of her fellow 104th compatriots. While withdrawing from Liberio during her group's attack on Marley to acquire both the Warhammer Titan's power and Zeke, Sasha is fatally wounded when shot in the chest by a stowaway Gabi and utters "Meat" with her dying breath. She is later revealed to have formed a close friendship, implied to be a romantic, with a Marleyan prisoner of war turned chef named Nicolo. In a blog published by Isayama, Sasha was named after the British actor and comedian Sacha Baron Cohen to make her character more comedic.

A hot-headed young man who speaks his mind, he initially planned to join the Military Police in order to live safely within Wall Sheena and manages to graduate within the top ten of his class, ranking sixth. He and Eren have opposing ideals; Jean thinks Eren is suicidal for wanting to join the Survey Corps and fight on the front lines, and throughout the manga has a simmering rivalry with him. In the battle of Trost, he leads a group of recruits to preserve the safety of the supply house, but is shaken that his decision led to the deaths of some of his comrades. After his close friend Marco dies, he changes his mind about joining the Military Police, and joins the Survey Corps instead. Jean later rises to become a commanding officer in the Survey Corps, and leads ground operations during the Raid on Liberio. He later intensely struggles with whether or not to stop the Rumbling or accept it and enjoy life in the Interior, but chooses to abandon his dream for the sake of saving the world, as he doesn't want his fallen comrades, particularly Marco, to be disappointed in him. Isayama has said that Jean was one of his favorite characters because he says what he thinks. Jean also harbors jealousy toward Eren because of Mikasa's apparent infatuation with him; it is heavily implied that Jean has a crush on Mikasa.

Ranked seventh of the trainee class, Marco is from the Jinae District and becomes close friends with Armin and Jean. He was known to be a 'goody-two-shoes' and aspired to join the Military Police so he could serve King Fritz, only to end up being killed under mysterious circumstances near the end of the battle of Trost. It is later revealed that it was due to him inadvertently overhearing Bertolt and Reiner talking about their Marleyan mission. Reiner tackles him and gives his vertical gear to Annie before leaving him to be consumed partly by a titan. Annie later uses his gear to cover up her killing of the captive Pure Titans, Sawney and Bean. Marco's death has a huge impact on Jean who subsequently abandoned his selfish attitude, as well as Reiner and Annie themselves, who still feel guilty about causing his death.

The 13th Commander of the Survey Corps, who led the last mission before the fall of Wall Maria, having served the government even after they murdered his father as a child believing it was for the good for the people to conceal the truth of Paradis' establishment. He also made the difficult choices for the benefit of others, which required him to sacrifice the lives of his men to see it through; he has a reputation for gambling everything on unorthodox battle strategies. A shrewd, bold and charismatic leader who encourages creative thinking among his subordinates, Erwin developed the Long-Range Scouting Formation, which substantially reduced the Survey Corps' death toll during its expeditions (Despite this, the Scouts continued to suffer significant casualties). After learning of a mole among the military ranks, Erwin concealed this intel from his subordinates while orchestrating the 57th expedition to expose and capture Annie. When Eren is kidnapped by Bertolt and Reiner, he leads a team to rescue him, having his right arm eaten by a Titan in the occasion. Once learning the government's actions were only for the benefit of the upper class, Erwin stages a bloodless coup d'état to place Historia into power. Erwin then leads an expedition to Shinganshina to seal the breach on Wall Maria, where he and his forces face the Warrior Titans. Erwin ends up being mortally wounded after resolving to sacrifice himself and the remaining recruits so Levi can attempt to kill Beast Titan. Levi initially saw injecting Erwin with the Titan serum as the logical choice until realizing that Erwin continually demonized himself on their behalf, deciding to let Erwin die in peace from his injuries when giving Armin the injection. Ever since then, Levi has been on a hunt for the Beast titan Zeke to fulfill his promise to avenge Erwin. Levi and him were together at the time of his death. He is voiced by Daisuke Ono in the Japanese anime, and by J. Michael Tatum in the English version.

The instructor who is in charge of training the 104th Corps recruits. His face and head are cleanly shaven except for a patch of beard beneath his chin. Before the fall of Wall Maria in the year 845, he became the 12th Commander of the Survey Corps and struggled to establish a base beyond the Walls, with no success. Following a particularly taxing expedition he suffered a mental breakdown and resigned his post to his successor, Erwin Smith, becoming the first commander to pass on his position without dying. He was close friends with Eren's parents; especially his mother, Carla, who he secretly loved. He was also the one to discover Eren deep in the forest after the Fall of Shiganshina, immediately following the moment when Eren's father passed on his Titan abilities to his son, and brought him back to safety.

Hange is a bespectacled Survey Corps veteran and the leader of 4th Squad. A scientist who studies the Titans, Hange shows little fear when interacting with them, and is thus ecstatic when initially meeting Eren. Hange had a strong hatred against Titans until the discovery of Ilse Langnar's notebook, which provided some new insight into the unknown nature of the Titans. Hange also invents new special weapons for the Scouts to use, such as a barrel that fires multiple grappling hooks to capture Titans alive, as well as the Thunder Spears, a weapon instrumental to the later successful recapture of Wall Maria. In the aftermath of the battle of Shiganshina, Hange's left eye is lost because of shrapnel caused by Colossal Titan's transformation and it was later covered up by an eyepatch. Hange succeeds Erwin as the 14th commander of the Survey Corps. Following Eren's message to all Subjects of Ymir, Hange forms an alliance with the remaining members of the Survey Corps and the Warriors to stop Eren. Hange ultimately sacrifices themself defending the members of the alliance from the Rumbling as they boarded the Azumabitos' flying boat. Before dying from burns and subsequent trampling, Hange successfully eliminates four Colossal Titans.