Keith "Instructor" Shadis

Keith Shadis is the head instructor of the 104th Trainee Squad. He seems to be a friend or have some sort of relationship with Dr. Grisha, as he knows that Eren is the son of the doctor and praises Eren for his effort.

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He is a former Commander of the Survey Corps, and was in command when Wall Maria fell in 845.

First Appearance Manga: Ch. 15 "One By One" Anime: Ep. 1 "To You Two Thousand Years Later" (Source: Attack on Titan Wiki)