The Master of Puppets is a future incarnation of the Master, if incarnation is the right word. They had run out of regenerations and were forced to transfer their mind and biodata into an appropriate vessel, specifically a puppet version of themself that they had specially crafted. They are capable of moving under their own volition, but require strings and a place to hang them for the best level of control; therefore, whenever they land in a new location, their first goal is to hypnotize an army of followers to do all the things they can't do (at least not well) in their wooden body. Their ultimate goal is to restore themself to their proper stature as a Time Lord, but they are perfectly happy to while away the time with smaller schemes in the meantime.