The Invaders was another one. Aliens who come to earth, surgically altered to look like humans so they can replace people and take over institutions. People would be replaced and start acting in peculiar ways that no longer made sense, as if their personality was sucked out and replaced with a new one. They look almost flawlessly human, but they get details wrong; their skin is often not quite right (if they replace a black man, the palms of their hands are black), they have no pulse or blood, and they can't move their pinky fingers because their original form only has three fingers and a thumb. They have to undergo regular treatment to maintain their altered form and even get corrective surgery later in the series, to fix the pinky finger problem. It was, like V, originally written with ideological infiltration in mind (though V was intended to be a warning against fascism rather than communism), but given troonery follows the same sort of patterns (infiltration and indoctrination to the point that a whole different personality seems to emerge), it works quite well as an analogy for troonism.
And then there's Invasion of the Body Snatchers. Both versions. REEEEEEEEEEEEE!