Flegel is a short young man who possesses a fairly chubby build. He has short red hair, freckles on his cheeks, and is usually seen wearing a regular gray coat with a white shirt, as well as a pair of black pants.
Flegel seems to be a very cowardly and impatient person. He complains about his father's decision to ally with the Scout Regiment without guarantee of their safety, and after his father's death at the hands of the Military Police, Flegel was so terrified that he was willing to resign himself to living in hiding in order to stay outside of the Military Police's reach, and was only convinced to take action by Hange Zoë.
With Hange's help, Flegel gained the motivation to fight against the Military Police. Since then, he has proven himself to be rather courageous, allowing himself to be used as bait to draw out members of the Military Police so that Hange could capture them. He has also proved to be rather cunning, being able to manipulate said MP members into admitting to the brigade's crimes in full view of the citizens of Trost. He is also shown to have his father's sense of loyalty, vowing to continue using the Reeves Company to protect the citizens of Trost.
Flegel accompanies his father and his father's associates to kidnap Eren Jaeger and Historia Reiss. Upon arriving at the warehouse where the two are being kept, the group is ambushed by members of the Scout Regiment, and Flegel is incapacitated.
After Reeves agrees to assist the Scout Regiment in recovering Eren and Historia, Flegel and his father lure two members of the Military Police into an ambush by Levi's squad. After the two policemen are captured, Flegel asks his father if the scouts will keep them safe, but his father is unsure. Flegel is appalled that his father would agree to help the scouts without guaranteeing their safety, but Reeves scolds him, telling him that a good merchant must be able and willing to find and pursue prospective profits, not just immediate gratification.
As they reenter Trost, Flegel has his father stop their carriage so that he can urinate in an alley. While Flegel is urinating, his father is ambushed and killed by Kenny Ackermann. Flegel stays hidden as Kenny leaves the scene, weeping in horror.
Flegel is later seen fleeing from Military Policemen. Turning into an alley, he finds himself at a dead end, only to be grabbed by Hange, who takes him to a rooftop using her ODM gear. She introduces herself and asks Flegel to explain the incident behind his father's death. Flegel explains how his father was killed by a tall man in a black coat, and Hange tells him that the two of them can work together to expose the MP, but Flegel refuses in fear of his life. Regardless, Hange forcibly takes him along with her.
Sometime later, Flegel is shown fleeing from a group of three armed Military policemen, who eventually corner him. One of the policemen tearfully thanks Flegel, claiming that he would have been killed for letting him escape. Before he shoots, Flegel panics and asks him why his father was killed. Although the policeman is confused as to why Flegel is asking questions at a time like this, he explains how Dimo betrayed the MP, insulting him in the process. Hearing this, Flegel adamantly states that the policeman does not understand anything, and that he chooses to have faith in the people that his father believed in. The policeman, angered by Flegel's words, yells that he should be begging for mercy like a pig, to which Flegel replies by telling him to look above.
Hange and Moblit drop down from the building, knocking out the policemen and saving Flegel's life. Many of the citizens in Trost emerge from the building, one of them saying that they have heard the truth about Dimo Reeves' death and all of them will attest to it. The policeman shouts at the crowd, threatening them and claiming that the news of the incident will not spread for more than three days, but is stopped by Flegel, who sits on his head. He vows to protect Trost and announces himself as the new CEO of the Reeves Company, much to the happiness of the citizens.