|Some dare call it|
An agent provocateur, or simply a provocateur, is a person who secretly infiltrates a group with the objective of weakening it from within.
As such they will, in reality, be representatives of another group opposed to the interests of their apparent allies. Their objective may be to create unrest, disunity or ill-will within the group while professing to hold the group's ideals to heart.
Alternatively, an agent provocateur may encourage the group to carry out crimes or other nefarious activities while secretly reporting their activities to their real masters (this would generally be a form of entrapment). It has often been said that the most outrageous advocate of crime and violence within an organization is likely to be an agent provocateur.
Many New Left groups from the 60s claim that they were brought down by FBI moles that acted as agents provocateurs. Some have sarcastically (?) claimed that unusually inarticulate or extreme conservatives, such as George W Bush are, in fact, liberal agents trying to discredit conservative values; see 'deep cover liberal'.
Conspiracy theorists will often decry others within their ranks who espouse a different variation on their pet theory as agents provocateurs. In the 9/11 "Truth" movement, for example, so-called "no planers" are often considered to be plants.
Agents provocateurs also make really hot lingerie.