-Hitler = part Jewish, tried to get rid of the Jews. Lord Voldemort = Father was a muggle (non-wizard), he tried to get rid of “Mudbloods” (People with non-wizarding blood)
-Hitler took over the German government. Lord Voldemort took over the ministry of magic.
-Hitler made himself immortal (at least his memory is) by killing millions of people. Lord Voldemort tried to make himself immortal by killing others. (In the books, he makes magical devices called Horcruxes which are infused with a piece of his soul. In order to fracture is soul, he has to commit murder, which is the only way to break one’s soul apart)
-Hitler tried to get the support of families with strong German heritage. Lord Voldemort’s supporters were from the oldest wizarding families.
-Both Hitler and Lord Voldemort could fly without the use of broom. (Okay that’s not true. Hitler needed the broom)
[Added a few days later] So in the wizarding world after Voldemort returned to power the Ministry of Magic started to register all people with non-wizard blood, and they took away their wands. This is kind of like how Hitler started with the concentration camps. No obviously murderous intent, just the desire to have these people registered, controlled and afraid.
I recently re-read the Harry Potter books, recently here meaning this summer after I returned from Germany. I read them with a new lease on the idea of a terrible leader taking power, which was when I noticed the similarities.
To my Knowledge, J.K. Rowling hasn’t come out and said that Lord Voldemort is Hitler, but there are certainly enough reasons how he could be.