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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 cheek bones, 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 was a serious man and a loyal Survey Corps member. He seemed to be a trusted subordinate, as he personally escorted and advised Erwin Smith during the the Corps' mission to Shiganshina.
Dirk is seen attending a meeting between Erwin and the other Survey Corps Squad Leaders 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 dismissed the notion, claiming Shadis was not worth it. 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.
After Eren successfully seals the hole in Wall Maria, Dirk and Erwin standby atop Wall Maria. Dirk is surprised to see that no one has attacks, 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 himself and his forces, Erwin orders Dirk's squad 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 Squad Dirk 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 himself.