Jagganth Daiki-Nagata was the leader of a human military rescue team in the 38th century assigned to investigate why all contact had been lost with the Le Verrier space station in orbit around Neptune. She had a habit of calling others "pet" and shooting anything that caused problems.
Upon encountering the Twelfth Doctor and Clara Oswald on Le Verrier, Nagata instantly assumed that they had something to do with the disappearance of the station's crew. However, with the Doctor's help she soon discovered that the truth: the crew had been consumed by their own sleep dust. Having taken the Morpheus process for granted whilst on Triton, Nagata was horrified to discover that the pods also evolved human sleep dust over time to become a sentient lifeform in the shape of the Sandmen. Aiding the Doctor in determining that whilst the lumbering Sandmen appeared blind, their visual receptors were being hijacked by the dust, she discovered that everyone who had used the Morpheus pods was now a spy for Gagan Rassmussen, who had been using the video to send a signal to create more Sandmen throughout the solar system.
Despite her young age, Nagata took her role as a leader very seriously and with dedication. She would often remind people that she was in charge when they tended to forget it. She was very loyal to the soldiers under her command and refused to leave them to die horribly until the Doctor convinced her there was nothing she could do.
While initially distrusting of the Doctor and Clara Oswald, she eventually grew to trust them, mainly because she did not have much choice and the Doctor proved to be very insightful when needed. (TV: Sleep No More)