This might be the scariest Twilight Zone episode yet. Dennis Hopper plays Peter Vollmer a street-corner neo-nazi whose rantings earn him contempt and beatings, and whose sole source of emotional comfort is...an elderly Jewish holocaust survivor named Ernst, who shows leniency towards Peter because he remembers him as a scared, abused child. This changes when the supernatural (?) element of the story is introduced: the ghost of Adolf Hitler shows up, cloaked in shadows, to instruct him on how to whip a mob into a frenzy better. As Hitler guides Vollmer towards success, what little humanity he has left in him is lost. His elderly mentor tries to pull him back, but it seems that it is too little, and too late.
This is one of the scariest episodes of The Twilight Zone, because it is one of the most relevant. Vollmer's lessons towards fascism are too realistic, and the sad story of a broken boy becoming an aggrieved, angry man are too familiar, and too realistic. It is possible that this episode has no supernatural element in it at all, that it is merely a psychological study of a man toying with fascism and getting sucked into it, his last good instincts being drowned out. The closing narrative of the story tells us what "He's Alive" means: that as long as the ideology of nazism is alive, it is the same as Hitler being alive himself. Whether the Hitler in this story was a ghost or a delusion is irrelevant, because the damage is the same.
The relevancy of the story to the year 2020, and the virulence with which xenophobia can spread to those who have a combination of inferiority or superiority, is too obvious to be explained explicitly.
As a somewhat funny note, other than Dennis Hopper, many of the actors in this story are Jewish. Three of the actors who play roles in Vollmer's neo-nazi squad, including Paul Mazursky, are Jewish. The actor who plays Ernst, Ludwig Donath, was a Jewish refugee from Europe, who also ironically played Hitler in several earlier movies. The actor who played Hitler was not Jewish, though. The director, Stuart Rosenberg, who later went on to direct Cool Hand Luke, is presumably Jewish as well. Rod Serling liked his little ironies.