An Emissary is a high-ranking servant of The Seven, to which they lend out their Keys of Kings. It is rare for one of these individuals to operate alone.
Spare keys operate under Highlander rules, being absorbed into other keys. The Seven do not lend out actual keys. The Emissaries draw power from the Seven themselves.
Jagganoth and Gog-Agog have none, while Solomon David has many.
Known emissaries include Emissary Saharus of the Celestial Empire, and a sullen and scarred guy next to Mottom. One may have been seen in Hell 71. Allison becomes the Emissary of Incubus. 000001 is Mammon's only Emissary.