Morgan Blue was a colonel in the Combined Galactic Resistance, which fought against the Daleks, and was the commander of the spaceship Aristotle. He was also the uncle of Journey and Kai Blue. (TV: Into the Dalek) When the Aristotle reported a high amount of Dalek activity in the Ryzak solar system, Morgan Blue was mentioned as its commander. (PROSE: The Secret Lives of Monsters)
When the Twelfth Doctor arrived on the Aristotle, Colonel Blue wanted to kill him in case he was a Dalek spy. However, Journey stopped him and convinced him that they were in need of a physician, mistaking the Doctor for a medical practitioner.
It was under Colonel Blue's orders that the Doctor, Clara Oswald, Journey, Gretchen Carlisle and Ross were shrunk to undertake an expedition inside "Rusty" and determine what had made him turn "good". When Rusty was fixed by the team inside, he sent a distress signal to his Dalek fleet, and the colonel led a group of resistance fighters in defence of the Aristotle. He was one of only a few soldiers who survived the attack. (TV: Into the Dalek)
Behind the scenes
In the script of Into the Dalek, Morgan Blue was described as "a tall tough man in his fifties".