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Keith Shardis (キース・シャーディス)Keith Shardis 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.
Manga: Ch. 15 "One By One"
Anime: Ep. 1 "To You Two Thousand Years Later"
(Source: Shingeki no Kyojin Wikia)