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Keith Shardis (キース・シャーディス)Keith Shardis was the head instructor of 104th Trainees Squad. He seemed to be a friend or have some sort of relationship with Dr. Grisha, as he knew Eren is the son of the doctor and praised Eren for his effort.
Manga: Ch. 15 "One By One"
Anime: Ep. 1 "To You Two Thousand Years Later"
(Source: Shingeki no Kyojin Wikia)