The Day the Earth Stood Still

Once Earth is visited by aliens who do destructive for all people. Aliens must exterminate humanity, because his presence is destroying the planet, and the Earth is one of the few planets that are suitable for the existence of complex organisms. Shortly before the planned destruction of mankind alien civilization decide to give people a last chance: they send to Earth his Envoy by the name of Klaata.

Klaata along with Gortom a biorobot, which is able to manage technical objects, arrive on the planet. Taking human form, Klaata is intended to bring the UN meeting and declare loudly on his mission, but the Americans, whose country he landed, denied this. Military plan to learn as much as possible about aliens and their technologies, therefore, Klaatu is questioned. This behavior is a recipe for self-destruction, but among the War turns out to be Dr. Helen Benson, whose forces all change.
A representative of an alien race that went through drastic evolution to survive its own climate change, Klaatu comes to Earth to assess whether humanity can prevent the environmental damage they have inflicted on their own planet. When barred from speaking to the United Nations, he decides humankind shall be exterminated so the planet can survive.