|Seriously Zofia?! You have faith in the fleet?! It took those imbeciles four years to control the seas! And guess what?! They lost half their damn ships doing it! Now they're telling us they're too chicken to attack till we take the fort?! Screw 'em all! They're pricks!|
|— Udo gets upset about Marley's Navy|
Udo was a boy of average height and build, though he was easily the tallest and heaviest of the Warrior candidates, with shaggy black hair and dark eyes which he wore oval-shaped goggles over in place of glasses. Like his fellow Warrior candidates, he wore the standard Marleyan soldier uniform consisting of a light jacket and pants, supply packs on the hip, suspender straps, a hard hat with a stripe around it, and tall combat boots. As an Eldian, his uniform was different from that of the Marleyans, as his shirt collar had a small badge with the Eldian star instead of a small clip and his hat had a white stripe with the Eldian star on it instead of a pure black stripe. As is law in Marley, Udo also wore the Eldian armband as all his family and ancestors residing there do as well.
Udo was not the most secure soldier nor did he possess a very level head. Like his other Warrior candidates, he was trained to aid the wounded and cared enough to come to Falco's aid, but his shaky nature sometimes caused him to neglect those he is treating. While he was not an excelling soldier, he possessed some margin of skill to have survived for four years in the Marley Mid-East War, he also seemed to be knowledgeable about at least one foreign language as he was able to comprehend and interpret the sayings of the wounded Mid-East Allied Forces's soldier.
On multiple occasions, he was shown to be frustrated about the harsh treatment that Eldians are forced to bear, either by his Marleyan superiors or by his enemies in the battlefield.
Udo and his fellow Warrior candidates participate in the Marley Mid-East War. When an injured Falco is brought back to the trench by his brother Colt Grice, Udo and the other Warrior candidates rush to his aid and begin treating his injuries and bandaging his wounds. During this time, Udo begins to panic in fear of their military failing and wraps Falco's bandages too tightly causing, Gabi to scold him.
When Falco returns to the trench with a wounded Mid-East soldier, Udo helps tend to the soldier's wounds. The soldier mutters something in a different language and Udo helps translate what he said.
After the battle, Udo is seen with the rest of the Warrior candidates in Fort Slava's harbor, watching as surviving Mid-East soldiers are sent back to their home countries. Udo grows angry, believing that the soldiers' war stories will only serve to demonize Eldians to the rest of the world, and begins lashing out at inanimate objects around him until Reiner Braun arrives. He is later seen at a party being held in Gabi's honor during the journey back to Marley.
Upon arriving at Liberio, Udo is reunited with his family. During training, Udo congratulates Falco for beating Gabi for the first time. On the way back to the internment zone, he enthusiastically shares the news with the soldiers and comments on how exceptional it is. Later that day, he watches the preparations for the festival with Zofia and Gabi.
At night, the candidates serve the ambassadors who came to Liberio. Hearing the guests insult the Eldians, Udo gets distracted and spills some wine on an ambassador from Hizuru. Terrified of being punished, Udo apologizes to her but she calms him down and covers up his mistake. As he asks her about her motivations, he is shocked to learn she helped him despite knowing he is an Eldian.
The following day, Udo enjoys the festival with his friends, and then joins the Warriors to listen to Willy Tybur's speech. When Willy reveals the truth about the Great Titan War during the play, Udo and his fellow Warrior candidates are stunned to learn that the 145th King, Karl Fritz was the one who put an end to the war.
When Eren Jaeger suddenly transforms into the Attack Titan behind the stage, debris is hurled into the audience. A flying piece of debris crushes Zofia. Shocked, Udo attempts to free her, but he is immediately trampled by the panicked audience members trying to escape Eren's Titan. Colt and Gabi recover his body, though Colt is unable to say whether or not Udo is dead. They rush Udo to the hospital amidst the chaos. At the hospital, the doctor refuses to give Udo a bed, saying that there is no space and he is already dead.
- Sketches of Udo included in the Attack on Titan: Final Manga Exhibition revealed that Udo was planned to have the full name Udo Bock (ウド・ボック Udo Bokku?).
- "Bock" is a style of beer that originated in Germany.