Mod Biscuits stated on the Official Runescape Forums that "The Gatekeepers were originally referred to as Mindslayers by the original developer of the fairy storyline. We still sometimes refer to them as Mindslayers even now. It's just an internal name we use for the Gatekeepers.". 
If you talk to the gatekeeper outside the shady grove, his name would appear as "Gate Keeper" in the chatbox.