Patient Zero (Sleep No More)
Never actually called this. Rassmussen called him "Patient Zero"
Talk about it here.
The first patient in the Morpheus program hadn't emerged from the pod until a reanimated Gagan Rassmussen released him on board the Le Verrier space station. Throughout his long sleep, so much sleep dust had formed in his eyes that it had completely enveloped him and transformed him into a Sandman. He was set loose on the Twelfth Doctor, Clara Oswald and Jagganth Dalkl-Nagata, but crumbled away into dust when the Doctor reversed the Le Verrier's gravity shields and escaped in the TARDIS. (TV: Sleep No More)
Abilities
The Sandman had the ability to control the other Sandmen, commanding them to surround the TARDIS and keep the Doctor and Clara out. It could also turn into dust at will but was weakened by the gravity shields.
