There are many characters in Attack on Titan that were introduced when they were a member of the 104th Cadet Corps. Floch Forster was a member of this class in the military, having trained alongside characters like Eren, Mikasa, Reiner, and Jean, but wasn't seen until the end of the Uprising arc.
Before that, he was a member of the Garrison, and though he practically didn't exist in the first half of the manga, he became a very important character toward the end as he developed into one of the antagonists the Survey Corps and Warrior Unit leading up to Eren starting the Rumbling.
10 He Joined The Survey Corps
The Survey Corps gained a lot more members once Historia became the queen of Paradis. One of them was Floch, who was excited about going outside of the walls and reuniting with the comrades he had before joining the Garrison. Since the Survey Corps was the most hated of the three military branches when the series began, it was surprising to see so many soldiers join them. Floch and the other recruits proved how much they changed within the first moment they were in the story by doing this.
9 He Followed Erwin's Orders
Though Floch was initially excited about being a member of the Survey Corps, his feelings quickly changed when the warriors attacked them in Shiganshina. He showed how weak of a soldier he was compared to those around him, hesitating to follow orders and panicking. He nearly defied Erwin's orders when the commander told him and the other soldiers around him that they would sacrifice themselves so Levi could kill the Beast Titan rather than waiting to die. However, Floch changed his mind and ended up being the only Survey Corps member to survive the charge.
8 He Was One Of The Few Survivors In The Battle At Shiganshina
Not only was Floch the only soldier to survive the charge towards the Beast Titan, but he was also one of the nine members in the entire Survey Corps after the battle ended, with Eren, Mikasa, Armin, Levi, Hange, Jean, Connie, and Sasha being the other eight.
The others had already had experience in real fights and survived countless times they could have been killed, and now Floch could understand where they came from and be seen as one of the most experienced soldiers, being a role model for newcomers the way that characters like Eren looked up to Levi and Erwin.
7 He Tried To Save Erwin's Life
After finding that Erwin was in critical condition but hadn't died, Floch tried to save his life. He knew that Levi had titan serum and that Erwin could survive if he was injected with it, so he carried the commander's body toward humanity's strongest soldier. However, Levi had just agreed to give the titan serum to Armin, who was also about to die. This caused the soldiers to argue over who should live, with Floch wanting Erwin to inherit the Colossal Titan despite thinking he was not a good person and being friends with Armin back in their training days.
6 He Became Eren's Most Loyal Follower
After Armin was saved, Floch wasn't afraid to voice his opinion on how Levi made the wrong choice. This caused him and Eren to strongly dislike each other. However, by the time the series jumped four years into the future, Floch became Eren's most loyal follower. Many of Eren's followers, the Yeagerists, were brought into the group by Floch, who also manipulated anyone he needed to in order to help Eren and gave the Yeagerists orders when Eren was unable to.
5 He Started Hiding Important Information
When Floch was first introduced, he would say whatever was on his mind and not hold anything back. But once he started working for Eren, he knew that if any information was revealed to someone who wasn't a Yeagerist, they would risk losing everything they worked for. Floch became very secretive and wouldn't even let one of Eren's friends know what they were doing. This was very similar to how Eren changed, as in the beginning of the series, he would also say anything he wanted to and not think of the consequences.
4 He Began To Celebrate His Victories
Floch, like many other soldiers who had transferred to the Survey Corps, were celebrating taking back the land in Wall Maria before they actually went on their mission. They thought that things would be completely fine and they'd all return as heroes. However, when Floch and the other eight survivors came back, he knew better than to celebrate.
Years later, when he helped Eren attack Marley, he encouraged everyone to celebrate since not nearly as many soldiers died. Neither one of these moments was an appropriate time to celebrate, seeing as how it was right before and in the middle of a battle that resulted in many deaths, but his reason to celebrate had certainly changed.
3 He Became Very Manipulative
Once the Yeagerists took over Paradis, Floch tried to manipulate people who weren't on their side to join him. The best example of this is when he told Jean that he could now join the Military Police, the branch that he had originally wanted to join when he was introduced. However, Jean came a long way since then, and even though there was still a part of him that wanted to live a peaceful, quiet life, he knew that he had to fight against Floch and Eren.
2 He Wanted To Hurt Anyone Who Didn't Agree With The Yeagerists
Floch would physically harm anyone he was not able to manipulate. Keith, the head instructor of the 104th Cadet Corps and former commander of the Survey Corps, taught Floch and a lot of other characters how to fight. But he never expected to have one of his students turn against him and force others to beat him up. Floch became a very violent person for anyone who didn't agree with Eren and join him in the fight against the rest of the world.
1 He Became A Great Fighter
Though he didn't have much skill on his first mission as a Survey Corps member, he was one of the strongest characters in Paradis toward the end of the manga, and not only because of his role as a Yeagerist. When the Survey Corps and Warrior Unit teamed up to chase after Eren, they needed to take a boat from the Yeagerists. They ended up in a huge battle in which they had to kill some of their friends from when they were in the 104th Cadet Corps, but Floch wasn't one of the ones to die. He was able to sneak onto the back of the boat and follow them, holding on for as long as he could. Once the Survey Corps and Warrior Unit got to the flying boat, Floch shot it, causing them to lose time. However, he finally died in the process. It took so long for them to kill Floch and even as he knew he was about to be killed, he kept his loyalty to Eren.