Doctor Waldman: You have created a monster, and it will destroy you.
Henry Frankenstein: He's just resting. Waiting for a new life to come.
Doctor Waldman: Whose life was one of brutality, violence, and murder.
Henry Frankenstein: Dangerous? Poor old Waldman. Have you never wanted to do anything that was dangerous? Where should we be if no-one tried to find out what lies beyond? Have your never wanted to look beyond the clouds and the stars, or to know what causes the trees to bud? And what changes the darkness into light? But if you talk like that, people call you crazy. Well, if I could discover just one of these things, what eternity is, for example, I wouldn't care if they did think I was crazy.
Henry Frankenstein: The brain you stole, Fritz. Think of it. The brain of a dead man waiting to live again in a body I made with my own hands! With my own hands.
Baron Frankenstein: Here's to health, a son to the house of Frankenstein... Here's to jolly good health to young Frankenstein.
Henry Frankenstein: Help! Help.
Villager #1: Listen, it's Frankenstein.
Villager #2: That way.
Victor Moritz: You're crazy.
Henry Frankenstein: Crazy, am I? We'll see whether I'm crazy or not.
Dr. Henry Frankenstein: The neck's broken. The brain is useless. We must find another brain.
Doctor Waldman: The brain which was stolen from my laboratory... was a criminal brain.
Answer: There seems to be no officially stated reason why the name was changed, but it's possible to theorise. There were numerous changes between the original book and the film. One theory is that these changes were to make the story more accessible to the mass audiences, and altering the name of the main character to a more common one could be seen as part of that. Another (possibly more likely) reason is down to alterations in the characters. Unlike the book, the film ultimately seeks to redeem Frankenstein's character, making him a more human and sympathetic character. Conversely, the character of Frankenstein's old friend, named Victor in the film, but Henry in the book, has been made a much less pleasant character. As Victor is quite a harsh, martial name and Henry comes across as rather more amiable, the filmmakers might well have decided that it would be more appropriate to the characters that they were trying to portray to switch the names round.
Tailkinker