I am Become Death, the Destroyer of Worlds
[This video] was filmed shortly after the [nuclear] bomb was created and he knew exponentially more powerful bombs would be invented. He lived through the second world war and witnessed Europe bombed over and over again. He had every reason to believe the next war, a nuclear war, was fast approaching and his creation would usher in the total annihilation of life on earth. This man literally felt he would be the cause of the annihilation of our species.
I remembered the line from the Hindu scripture, the Bhagavad-Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, “Now I am become Death, the destroyer of worlds.” I suppose we all thought that, one way or another.
Oppenheimer and the Gita by Alex Wellerstein