Thomas Wagner 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 had blond hair with pronounced sideburns, and was usually seen wearing the standard trainee uniform or simple casual attire when off-duty.
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.
Appearance: Thomas had blond hair with pronounced sideburns, and was usually seen wearing the standard trainee uniform or simple casual attire when off-duty.
Personality: 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.
Thomas Wagner in the story: 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.
How Thomas Wagner echoes later: While speaking to Historia under the Reiss Chapel, Eren mentions Thomas as being among the victims he and Grisha Yeager were responsible for killing by stealing the Founding Titan. During the Survey Corps feast before the battle of Shiganshina District, Eren remembers of Thomas at the time Sasha stole meat.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.