They’re all the segments, or it could be also said clones of the Dottore, one of the Fatui harbingers.
Alpha: the oldest and calmest one, rational. No mask, long wavy blue hair, red eyes. 
Gamma: weird, crazy, cruel. Wears black mask on the side of his head, short wavy blue hair, red eyes, many scars. Gamma is failed prototype, so his mind is corrupted slightly, showing his madness.
Omega: rational, cold, aloof from others. Black mask, wavy blue hair, red eyes. Imitating Dottore, his creator.