Every single one of the four long seasons of Attack on Titan features characters who are just introduced, deeply expanded upon, or unfortunately killed. While the main Scout Regime and the main antagonists are given detailed backgrounds and critical roles in the story, some unlikely minor characters end up becoming the key players in the grand scheme of things. The Attack on Titan minor characters who changed the course of the story through their brave actions deserve a little more recognition!
These characters are credited for critically influencing the main cast, teaching important lessons to others, or even setting off a domino effect of actions that change the ending of Eren's story. All of the characters in Attack on Titan are there for a reason, even the ones who didn't survive until the end.
Warning: Spoilers Ahead
8 Marco Bodt
After getting a closer look at the young Scouts who end up fighting by Eren's side until the end of the anime, it is clear that sweet Marco didn't make the cut on the main character list. He is introduced as a member of the 104th Cadet Corps alongside the main crew and possesses excellent skills, intelligence, and leadership abilities on par with Jean, Connie, and the others. However, his life was cut short by the infiltrating Warriors: Reiner, Bertholdt, and Annie.
His death changed the lives of many of the young cadets. The Warriors all suffered deep emotional scars from having to kill their new friend. Jean was traumatized from losing his best friend and the main characters refer to Marco's death continuously over the next three seasons. His positivity inspired Jean to join the Scouts and his death helped Reiner flip allegiances later down the line. It's heartwarming to see the characters never forget Marco's impact even years after he died.
7 Keith Shadis
Shadis is the head commandment of the Cadet Corps where he trained the main characters to become Scouts. He was just a strict and strange commander during his time in the first season and no viewers expected to see him again. However, he reappears in the third season as a person with key information about Grisha Jaeger and the truth of Paradis.
He had found Grisha when he just arrived to Paradis and they continued to be friends for years. He was the one who reunited Grisha with Eren after the breach of Wall Maria, which resulted in Eren getting the power of the Attack Titan. Shadis continues on training scouts and refuses to join the Jaegerists to protect the island's youth.
6 Nicolo
Nicolo is a Marley citizen who is kidnaped and put to work as the chef on Paradis. He falls in love with Sasha and becomes acquaintances with the Subjects of Ymir. After Sasha's death, Nicolo meets her family and asks if he can cook for them someday. That someday comes and he, along with the other main characters, is faced with the situation of drinking Zeke's contaminated wine.
Nicolo stops Jean and the others from drinking it, with only a feeling that it's contaminated, saving them from turning into Titan in the following days. He helps the Brauns escape during the attack on Shiganshina and allows Gabi to live on safely. Nicolo contributed to the prolonged lives of many of the main characters during his time in the final season.
5 Floch
Oh, Floch. This unhinged young man was first introduced in season three as a new member of the Survey Corps. He is thrown into a suicidal battle where no one is predicted to survive and must gather all the bravery he can to fight to the death. Though he doesn't seem to have a big importance in that season, he miraculously survives the battle and carries on with the Scouts.
It isn't until the next season that viewers get to see just how important this new character really is. He becomes infatuated with Eren's ideals and leads the Jaegerist movement across Paradis, using whatever means necessary to overthrow the government and get Eren in power.
4 Grisha Jaeger
Though Grisha is one of the most important figures in the entire series, he technically isn't a main character. He only appears alive in a few episodes, having died since Eren was a young kid. His whole situation is a total mystery until the end of the third season when the main cast finally reach the Shiganshina basement.
Grisha, motivated by his own beliefs and goals while also being influenced by his Titan-shifting son, leads the entire world on a path to destruction. He set everything in motion, from his time in Marley to stealing the Founding Titan to giving the power to young Eren. Grisha is the reason that everything in the series happened the way it did.
3 Mrs. Springer
This incredibly minor character never even made an appearance as a living person before they are debuted as a Titan. However, Connie's mom sets off a domino effect of actions, starting from when Connie realizes that is his mom. The Scouts then deduce that there's a way to change humans into Titans and that all the Titans they have killed were once Subjects of Ymir like them.
She returns in the fourth season when Connie wishes to sacrifice Falco to bring his mom back into human form. The grim situation she is faced with causes a lot of trauma for Connie, but leads to his important personal growth.
2 Hannes
There's no denying that Hannes went through a great deal of character growth, even as a side character who only made occasional appearances in the series. He starts off as a drunk guard who slacks off at work and can't gather the bravery to save Eren's mother from a Titan. After years of guilt, he sacrifices his life to save Eren and Mikasa, something he wouldn't have been able to do years prior.
His death gave Eren just enough time to heal his hand so that his connection with Dina's Titan would be effective. That one moment, that one touch, resulting from Hannes' sacrifice, changed the entire trajectory of the series' main plot.
1 Louise
No one expected to see this young girl after her first appearance in season one. After Mikasa saves her life in the breach of Trost District, she is inspired to join the Survey Corps to make a difference just like Mikasa did.
She ends up defecting to be a part of the Jaegerists and leaks information about Eren's arrest to the public, sparking the rise of the Jaegerists rule on Paradis. She made a valiant return to the story after first appearing as a small girl needing help.