We've seen before how Mark Rosewater carries with him a piece of well-worn paper to jot down Magic card ideas. One of these ideas was "Helm of Volrath," the card that eventually became Mirrodin's Mindslaver.
Mark Rosewater's design notes: "Helm of Possession"
In this scan you can see that he titled the card "Helm of Possession" in his notes; it was to become a splashy "marquee" card for Tempest. Instead the name Helm of Possession, and the concept of a powerful helm belonging to Volrath, became attached to this creature-stealing artifact:
The basic turn-stealing mechanic eventually wound up on Mindslaver. Interestingly, as you can see from its art, Mindslaver was still concepted as a mind-control helmet.