Most theories floating around about who Doppelganger has impersonated aren’t grounded in much evidence. We have yet to see if any additional trickery from the Supe is shown later in season 2. Given that his neck was snapped in that cabin, it is unlikely that any more deep cover revelations will present themselves. The Boys could give us some flashbacks involving Doppelganger, but that feels a bit cheap as far as surprises go. So far, Eric Kripke and his writing team have shown us that they aren’t a fan of using predictable tropes.
So far it looks as though Doppelganger has only appeared in two episodes. Not only did he doppel Madelyn Stillwell for a thirsty Homelander, but he also appeared in an episode entitled “Cherry” way back in season 1. At that time, Vought was fighting to get Supes into the military, and Stillwell used the shapeshifting Supe to blackmail a senator. Doppelganger posed as a young woman and lured the senator into a hotel room where he snapped pictures of the two of them in a compromising position. Classic Vought.
With all the possible implications that come with impersonations, we are surprised that Doppelganger hasn’t been used more often, though it is possible that Kripke sees these kinds of cheap twists as a hallmark of lazy writing. Digging through the comic book source material has shown zilch as far as appearances from the shapeshifter go. It looks as though the tubby sneakster has reached the end of his story, which is a good decision. We wouldn’t want things to get predictable.