|Eren...you don't know it yet, but you'll probably find out soon...why Erwin Smith leads the hope of humankind, the Survey Corps.|
|— Eld urges Eren Yeager to trust in his superiors|
Eld had long blond hair which had a middle parting and a bun folded at the back to keep his hair tied. He also had a small beard. Like most other Survey Corps members, he wore a green cloak with The Wings of Freedom emblem on the back. He wore the same uniform as the other Corps soldiers.
Eld was a responsible and firm leader with a strong sense of duty. He did not talk much, but when he did, he spoke bluntly and in a straightforward manner. He also seemed to have been a veteran of sorts as he teased Petra Ral and Oluo Bozado about having wet their pants on their first expedition, and sarcastically referred to them as "fine fearless soldiers." He also seemed to hold some sort of belief of what makes a true soldier, as he lectured Oluo that a kill record alone does not make a great soldier.
When Eren accidentally transformed, he seemed to have been more concerned about the reasoning as to why and demanded an answer from Eren. His reaction was interesting in comparison to his comrades; Oluo threatened to kill Eren, Petra feared for Levi's life, and Gunther demanded evidence from Eren about his transformation and intentions.
Along with the other members of the Special Operations Squad, he had some remorse over his reaction to Eren's transformation as he bit his hand just like Eren, which symbolized a bond between them.
After the post-Trost District battle trial to decide Eren Yeager's fate concludes with Eren joining the Survey Corps, the Special Operations Squad, is assigned to look after Eren. Eld, along with the rest of the squad, accompanies Eren to the former HQ of the Survey Corps, which will now serve as a hideout for Eren. After their arrival, Eld and Gunther notice that the HQ has not been properly maintained due to being unused. Due to that, Levi orders everyone to begin cleaning. Later that day, while the squad discusses the upcoming expedition, Hange arrives and Eren asks them to explain their experiments with Titans. Gunther and the rest quickly leave the room, already painfully familiar with Hange's long-winded speeches about Titans.
The next day, Eld, along with the rest of the soldiers, arrives to the crime scene after being notified about the killings of Sonny and Bean. After the investigation is done and the culprit is not found, Eld and Gunther discuss the upcoming induction ceremony, asking Eren whether any of his classmates will join, but Eren is unable to answer with certainty. Eld is then present at the said ceremony, listening to Erwin's speech.
Levi finds a way to contain Eren in his Titan form without killing him, allowing Hange to run experiments on him, which Eld and the rest of the squad monitor. Eren is unable to transform for some reason, but later triggers his transformation while attempting to pick up a teaspoon. Eld and the rest of his squad mates immediately prepare to kill Eren, believing he has betrayed them, but Levi keeps them at bay. Later, Hange reveals to everyone the secret behind Eren's transformation. Realizing their mistake, Eld and others bite their hands as a form of punishment, showing that they can trust each other.
One month later, Eld is part of the expedition that heads into the Titan territory. As time progresses, the news of a mysterious Titan killing the soldiers reaches the Levi Squad just as Eld and others witness the black smoke signal, knowing that an Abnormal. Titan is near their position. Eventually, they enter the Titan Forest. Eren questions this, but then notices Eld and others also do not know what is going on. At that moment, the mysterious Female Titan reaches their location. As they are being chased, Eld and the other squad soldiers beg Levi for orders, proposing to take the Titan down as it slaughters the reinforcements from behind. Levi, however, just shoots a sound grenade to calm them down, reminding them of their job. Eren finds himself to be unable to comply with the orders as he watches more soldiers to be killed. His intentions are made clear when he is about to bite his hand. Levi tells him to choose whether he believes in himself or the squad. Eren decides to go with the squad, and as the Titan is about to catch up with them, they reach the location of Erwin and other soldiers who manage to trap the Female Titan, much to the surprise of Gunther and the squad. They then brag to Eren, claiming that it is thanks to the power of the Survey Corps that they managed to capture their foe.
Afterward, Eld and others discuss Erwin's decision not to tell the soldiers about the plan. Eren wonders why is it that not even the elite soldiers were told about it, angering Oluo and Petra, but Eld agrees with Eren, stating that Erwin must have had a reason. They realize that if they answered Erwin's mysterious question back then, they would probably be trusted enough to be let in the operation.
Seeing a flare that indicates the regiment is retreating, the squad begins making their way out of the forest. On their way to rejoin with Levi, Eld teases Petra and Oluo for peeing their pants on the first expedition. They notice another signal flare and thinking it is shot by Levi, they fire their own one. However, the mysterious soldier kills Gunther and then transforms into the Female Titan to resume her pursuit of Eren.
Eren is ordered to flee while the surviving squad members engage the Titan in battle. The squad seems to have the upper hand, with Eld launching an attack and a smoke screen blinding the Titan that allows Petra and Oluo to take out her eyes. Eld then launches several attacks on her arms before Oluo and Petra joined in, severing them and rendering them useless. As Eld and Petra move in for the kill, the Titan suddenly regenerates a single eye and bites Eld in half, also severing his arm. Eld's upper half is thrown to the ground as the Female Titan engages Petra and Oluo, killing them both while Eren looks on in horror.
Later during the Battle of Shiganshina District, as Erwin Smith begins to lament the dwindling hopes of his dream, Eld stands among the many fallen Survey Corps soldiers in Erwin's mind, wanting to know if their deaths had meaning.
In the forest, as Levi contemplates all the times he risked his life to save Eren, Eld appears among the comrades he had lost along the way.
When Hange decides to oppose Eren's plan to destroy the world beyond the Walls, Eld is one of the soldiers Hange remembers when arguing that their fallen comrades would not support destroying the world.
Eld was a very adept warrior who had a very high kill record of 46 Titan kills (of which 32 were with a team and 14 were solo). He also seemed to have been very proficient with the vertical equipment, using fake-outs with the steel wires to propel himself backwards during an attack in combination with using the vertical equipment to help him brake while simultaneously using the gas exhaustion as a smokescreen to blind a Titan and support his comrades' attack. He was very skillful when using his blades to bring down the Female Titan's arms, as shown by him using a variety of different attacks.
Eld Jinn's statistics as of year 850:
Eren Yeager - Eld held respect for Eren as a fellow member of the Special Operations Squad, and recognized the value he held for humanity. He was initially doubtful of Eren but grew to trust him, biting his hand after a misunderstanding in apology for not believing him.
Levi Ackerman - Eld was shown professional respect by Levi, who placed him as the second-in-command of his squad. Eld trusted the captain and was completely loyal to him, willing to trust his orders even when not understanding the reasons.
Gunther Schultz - Eld and Gunther were close comrades and shared a good relationship. Both were highly skilled in killing Titans such that they were selected as members of the Special Operations Squad.
Petra Ral and Oluo Bozado - As comrades, they worked together and shared great faith and friendship. Their relationship was friendly, able to joke around even when out on expeditions. Their impressive teamwork was noted by Eren during the time they engaged the Female Titan.
- Eld tied with Ilse Langnar for forty-ninth in the Second Character Popularity Poll.
- Eld ranked thirty-forth in the Third Character Popularity Poll.
- Eld’s name in Old Norse means ‘flame’ , ‘fire’.
- His name in Middle English(Old English) means ‘old’