Hector Quell was the captain of the Orient Express. A former soldier, he suffered from post-traumatic stress. After Mrs Pitt and a chef were killed, the Twelfth Doctor confronted Quell about taking action. He refused on the basis that he had already followed the protocols for accidental death, not believing the Doctor's claims that the Foretold, a mythical mummy, was responsible.
When one of his guards was killed, he accepted the Doctor's theory. The scientists about the Express discovered that it was targeting the weak, and the Doctor informed Quell that his mental issues made him the next target after Professor Moorhouse.
When the Foretold came for him, he fired upon it, claiming he would be a poor soldier not to do so, even though he was aware that the gesture would not harm the Foretold. Quell remained impressively calm as the Foretold approached, describing it and it's actions as clearly as he could in the time he had, up until his final second. As it moved to kill him, he thanked the Doctor for "waking him up" and considered his demise a good death as he would die facing the enemy, like a soldier. (TV: Mummy on the Orient Express)