Keith 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.

First Appearance

Manga: Ch. 15 "One By One"

Anime: Ep. 1 "To You Two Thousand Years Later"

(Source: Attack on Titan Wiki)