Godzilla (1954) directed by Ishiro Honda

In 1954-55, two films were released in Japan that commented on the fear and paranoia of nuclear annihilation in Japan. One was I Live in Fear (1955) directed by Akira Kurosawa about a Japanese business owner who goes insane by the threat of nuclear war. The other film was by Kurosawa's frequent assistant director Ishiro Honda and deals with a creature spawned by nuclear fallout taking revenge on humanity. Godzilla (1954) was not the first "kaiju" or giant monster film, but its impact has been the most long-lasting. It has used the threat of these un-natural beings as direct allegories of man's appetite for destruction alive in the public consciousness since 1954. 

The nuclear testing on the Bikini Atoll and the nuclear fallout that affected the Japanese fishing boat Lucky Dragon No. 5 were the immediate catalyst for this film, but the atomic bombings of Hiroshima and Nagasaki are obviously the event shadowing the whole film. One may be surprised at how much of the codifiers of the Godzilla franchise was established in this film. Despite the very 1950s special effects, the narrative and seriousness of the this film is still the best of the franchise. Of course, the longest lasting aspect of this film is Godzilla's iconic roar. Also the political commentary has also remained a feature of the franchise, more or less. I'd guess that the Cold War balancing at Japan was engaged in and public opinion to the Luck Dragon Incident deeply informed this film. This movie is the cornerstone of the idea of a man-made apocalypse; if you take Godzilla out, a lot of the devastation you see in this movie still have real-life analogues–that's what makes this movie endure to me.

Some afterthoughs: It is interesting to think the Takeshi Shimura had starring roles in the two biggest Japanese movies of 1954: this and Seven Samurai. Half the crew of this film (especially the special effects crew) were war criminals associated with the wartime ministry of propaganda. The Godzilla suit was by all accounts the most hellish thing on Earth to work-in at that time (this was before Toho Studios has air-condition).