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Prior to the final updates in MSN Messenger there was Live Plus Messenger and for some time there was an "identity thief" program where you could copy the avatar, name, and appearance of a friend's account on the fly in chat, it made an entertaining impersonation session where you could go in and swap with someone and play different parts. It was actually rather fun because sometimes the person's being talked to couldn't tell the difference between the original user and the fake user.
In TTT on Garry's Mod, I had the same concept commissioned in what I called the "doppelganger" item for traitors. You could either while another person was alive, pass by someone while they were alive and record their identity, role, and player model or if they died and were not discovered, you could either cause a living person to be blamed for events that occurred or you could play the part of a dead man that appears to be alive still. It was one of my favorite ways to go about the game, especially when using the microphone as another person that normally did not use a microphone