Sleeper agent
From Tardis Wiki, the free Doctor Who reference
Sleeper agents are soldiers used before an invasion. They are often modified to resembe the species that is to be invaded, and are used to gather intelligence on the species and planet.
The sleeper agents of some species had implants which could take the information and transmit it to the main invasion fleet. Some inplants even had built-in weaponry such as spikes and explosives. (TW: Sleeper)
