The Puppet Masters

Published in 1951, the novel follows a secret American government agency tasked with combating slug-like alien invaders. These parasitic creatures attach themselves to human backs, taking total control of their nervous systems to infiltrate society.

Yes, the novel was adapted into a 1994 film of the same name starring Donald Sutherland. The movie attempted to capture the 1950s alien invasion paranoia present in Heinlein's original text.

While both stories explore themes of alien assimilation and paranoia, Heinlein's novel was published in 1951, predating the famous "Invasion of the Body Snatchers" novel. Heinlein's invaders are visibly attached to their hosts, prompting a more aggressive, militaristic response from the government.

Yes, like much of the science fiction produced during the early 1950s, the novel is widely interpreted as an allegory for Cold War fears regarding communist infiltration. The mind-controlling slugs represent the perceived loss of individualism and free will.