Hoover, Bertolt

Bertolt Hoover originally joined the military with aspirations of joining the Military Police and living in the safety of the inner wall.

After seeing Eren's determination and desire to join the Scouting Legion, he considered himself a coward for wanting to get far away from them. Eventually he graduated in the top ten of his class coming in at third place, and joined the Scouting Legion.

Major spoiler:

[Spoiler] Later it is revealed that he is the Colossal Titan who broke through Wall Maria and infiltrated the walls as a spy. [/Spoiler]

Major spoiler:

[Spoiler] During the Survey Corp's attack on Shiganshina in the operation to retake Wall Maria, he kills most of the soldiers inside the city when transforming and finds himself in a battle against Eren and Armin. In this fight, he is defeated by Eren, Bertholdt's body is then brought to Captain Levi, who decides to use the Titan Injection on Armin, who nearly died to the burns and wounds he suffered during the fight earlier. Armin's pure Titan eats Bertholdt as he screams for Annie and Reiner to save him. [/Spoiler]

Note: Bertolt Hoover is the official English translation by Kodansha.