Doppelganger is an informal designation to archons who adopt a deep undercover identity to do a specific job.
These very deep-cover agents are all masters of disguise, impersonation, and intelligence gathering, both of the mundane variety and through mastery of Disciplines such as Auspex, Dominate, Obfuscate, and - in the case of one specific archon, if hearsay is to be believed - Vicissitude. Most doppelgangers have willingly gone through intense indoctrination and mental conditioning to avoid giving themselves away under questioning, torture, and even Dominate, and nearly all are blood bound to their justicar to further strengthen their ties of loyalty.
Although doppelgangers are sometimes used to gather intelligence on the Sabbat or other non-Camarilla factions and clans like the Followers of Set, the justicars and the Inner Circle normally prefer to risk less valuable agents than archons in such endeavors. By far the most common operation undertaken by a doppelganger is internal security, gathering information on the activities of Camarilla Kindred . This most frequently focuses on princes and other elders in positions of authority, though doppelganger presence among anarchs is not unknown.
The favored technique of a doppelganger is to observe a particular individual who is already a close ally (or believed to be a close ally) of the Kindred under suspicion. This individual is studied and researched until the archon believes she can pass herself off as that individual convincingly and under moderately close scrutiny. At this point, the subject is "removed from play" (a euphemism that usually means staked and stuffed into cold storage until the exchange act is complete, though some who were deemed guilty of sufficient wrongdoing against the Camarilla are simply executed), and the doppelganger takes her place . In this fashion, the archon can quickly get close to the true target of the investigation and uncover details that could not be learned through other means . Some of the most successful doppelgangers have spent years in an undercover identity without being exposed.
Even the most well-trained and alert observer cannot learn every detail about a subject, of course - if they could, there would be no need for doppelgangers at all, for they could learn all they needed simply by studying their primary target. Charades of this nature unravel as often as not, even when attempted by the best of the best. For obvious reasons, many other Kindred who have heard of them loathe doppelgangers with a violent passion. A doppelganger whose true identity is exposed had better have one hell of a tight escape plan set up, since the odds are overwhelming she'll be dead before the night is out.
- Archons & Templars, p. 20-21