Dirk was a man of average height and build, with long, blond hair that he kept pushed back out of his eyes. He also had a thin beard on his chin and cheekbones, and a small mustache. When not wearing the standard Survey Corps uniform his attire consisted of a white button-up shirt, dark pants, and a black vest.
Dirk appeared to be a rather calm, serious man. When violence erupted among the other soldiers, Dirk only made a casual note of their behavior, and made no effort to break up the fighting or intervene in any way. He seemed to be a trusted subordinate, as he personally escorted and advised Erwin Smith during the Survey Corps' mission to Shiganshina.
Dirk is seen attending a meeting between Erwin and the other Survey Corps officers to discuss the recent revelations involving Eren Yeager's father Grisha. After the meeting, Dirk suggests possibly punishing Keith Shadis for withholding information from the Military, but Hange Zoë dismisses the notion, claiming that Shadis is not worth the effort.
Later, Dirk can be seen watching with his fellow leaders as the Corps' soldiers fight each other for the meat that is being served in celebration of the mission recapture of Wall Maria. Although Dirk takes special note of the violence that begins erupting as a result of the meat, he is not concerned enough to try to stop it, choosing instead to ignore the brawls.
The day of the operation, all soldiers are ready at dawn. Dirk and other high-ranking soldiers salute to members of the other branches and head to the Wall. However, the soldiers are surprised after seeing that the civilians know about the operation's goals and start to cheer for them. Although they are initially annoyed that word of their departure has spread, they are silenced by the sight of Erwin, ecstatic to have such fanfare for the corps, cheering along with the civilians.
Near dawn, the Survey Corps walk on foot through a forest on a mountain, leading their horses. Dirk is questioned by Levi as to how much longer it will take them to reach the bottom of the mountain, and Dirk assures him that they are nearly there. Eventually, they reach Shiganshina District, and as Eren seals the hole in Wall Maria, Dirk and Erwin standby atop the Wall. Dirk is surprised to see that no one has attacked, and wonders if the Corps' forces are too much for Reiner and Bertolt to handle. He is interrupted by the arrival of Armin Arlert, and is shocked to learn that Armin has found evidence of a third person accompanying Reiner and Bertolt. After Erwin gives Armin command of the Survey Corps so that he can look for Reiner and Bertolt, Dirk comments on the big gamble Erwin has taken, and asks if the Corps will be staying until Reiner and Bertolt are found, which Erwin confirms.
When the Beast Titan reveals itself and its forces, Erwin orders Dirk's team to meet up with Marlene and Klaus' squads, to protect the Corps' horses. Dirk and his fellow soldiers fight off approaching Titans while the recruits in his team take the Corps' horses to a safe place. After finishing the Titans on his side of the battlefield, Dirk reports to Levi that only a few Titans are left, and urges Levi to rest while he and the rest of the soldiers handle them. However, before he can engage any more Titans, Dirk and his teammates are cut down by a barrage of rocks thrown by the Beast Titan. Dirk, managing to survive the first wave of rocks, only has time to observe the corpse of one of his allies before being torn to pieces by a second barrage of rocks.