Thomas Wagner (トーマス・ワグナー Tōmasu Wagunā?) was a graduate of the 104th Training Corps who fought during the battle for Trost District and was assigned to the middle guard after the Colossus Titan's second attack.
Thomas was initially quite pessimistic about defeating the Titans, believing that humanity ultimately stands no chance, but he would later change his way of thinking after hearing an inspiring speech from Eren. As a trainee, Thomas admitted to still being a bit cowardly, as he was too frightened to immediately act upon witnessing the Colossus Titan for the first time. Despite this, Thomas was also somewhat of a leader, rallying his team into turning their first battle into a hunting competition despite the inherent uncertainty.
On the first night of his time in the 104th Training Corps, Thomas and his fellow trainees swamp Eren Yeager with questions about the Fall of Wall Maria after learning that he is a survivor from Shiganshina District.
When Eren retakes his Vertical maneuvering equipment aptitude test, Thomas is put in charge of operating the training equipment for the test. Eren fails again, and Instructor Shadis orders Thomas to lower him down and exchange harnesses with him, revealing that there is a defect in Eren's.
On the night of the 104th Training Corps's graduation ceremony, Eren and Jean Kirstein get into a fight over their respective choices for which branch of the military to join. Eren's passionate words on behalf of the Survey Corps inspire Thomas to consider joining the corps as well.
The following day, Thomas's squad is assigned to clean out the cannons atop Wall Rose. As they are working, Thomas reveals to Eren that his words the previous night inspired many of his fellow trainees to consider joining the Survey Corps. Their conversation is interrupted by Sasha Blouse, who reveals that she has stolen meat from the officers' lounge. Despite some reservations, Thomas agrees to partake, celebrating the idea of retaking Wall Maria soon.
Their festivities are cut short when the Colossus Titan appears outside Trost District, knocking them off the Wall with a blast of steam. Eren orders them to attack the Colossus Titan, but Thomas and his comrades are too shocked to immediately react. When they finally climb back to the top of the Wall, they find that the Titan has vanished under a cloud of vapor. Thomas commends Eren for trying to attack the Titan as the Garrison's advance team arrives, and the trainees are ordered to return to HQ.
After the breach, he is assigned to the middle guard along with Eren, Armin Arlert, Mylius Zeramuski, Nac Tias, and Mina Carolina. He suggests they have a contest on who can kill the most Titans. Noticing the alarming amount of Titans in the middle guard, the squad begins to advance, but an abnormal Titan surprises them, catching Thomas it its mouth and swallowing him whole, while his team mates watch in horror.
Armin would later report his demise to the remaining members of the 104th Training Corps, saying he died valiantly in the line of duty.