Dieter was a man of average height and build. He had a welcoming face with a mustache and also had a beard around his jawline. He was notable for the white bandanna that he wore around his head, which concealed his bald spot, but showed light brown hair along the sides and back. He was never seen without the standard Scout Regiment Uniform, but he did add the green cloak during expeditions.
Dieter was a serious leader who never took his job lightly. At the same time, he truly cared for the new recruits and wanted to make their first expedition as easy as possible for them. This was proved as he was the one who taught them about the Long-Distance Enemy Detection devised by Erwin Smith. Dieter was not a fan of fighting Titans and always tried to stick to the idea of avoiding them outside the Walls, however, he never hesitated to fight them when it was necessary.
He also had a more lighthearted side, as was shown when he thanked his horse for coming back to him.
Dieter Ness is shown introducing himself to new recruits that joined the Scout Regiment and remarks that his horse, Charrette, likes to chew off hair. He is later shown teaching the recruits about Erwin Smith's long distance enemy scouting formation in a class room.He appears as an instructor and unit leader in the expedition mounted from the Calaneth District into the Titan-infested lands outside Wall Rose. He encounters an abnormal Titan in a field, and uses his omni-directional mobility gear to sever the Titan's ankles, causing it to fall over and allowing his squad mate Luke Cis to destroy the nape of its neck. To his joy, Dieter's horse returns for him, and he and Luke resume the expedition. Almost immediately after, however, they encounter the Female Titan, who he believes to be an aberrant, and is much faster than any Titan they have ever seen before. Caught by surprise, Dieter is almost squashed by the Titan's enormous foot and both he and Luke charge for its nape. However, the Female Titan easily intercepts Luke, crushing him with no effort, and swiftly catches Dieter's line before whipping it to the ground, killing him instantly.