"Preston Garvey" is an impersonator of Preston Garvey, a Minutemen senior officer. He will ask for 100 caps to help the Minutemen. The Sole Survivor can give him caps, refuse, say that they are the general (which may or may not be true, depending on their faction choice), or reveal that they know the real Preston Garvey.
Having the real Preston Garvey as a companion will not change how this encounter plays out; neither of the Prestons will even acknowledge each other.
Once the scene has been played through without violence, his character name in V.A.T.S. will change to "Preston Garvey Impersonator," and he will run away. If the player character attacks the impersonator while he is running, he will become hostile.
Killing him has no negative effects.
Appearances[]
The Preston Garvey impersonator appears only in Fallout 4.
Behind the scenes[]
The impersonator's Editor ID (RETravelSC03_PrestonGarveyImpersonator) indicates that he and his random encounter were created by level designer Steve Cornett.