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First 7 are Universal Classic Monster, 8. is included in several Universal movies, while others are classics from various movies. Each of them belongs to specific type of monsters with some exceptions, so list will be versatile and could fit different tastes.
1. Dracula - Classical vampirism. And first association is Bela Lugosi and iconic Dracula. Later, we got tons of such movies. Man in ,,traditional vampire" elegant suit, drinks blood and has plenty of abilities such as hypnosis, transforms into bat, enhanced strength and so on. And some of weakness of course.
2. The Wolfman - That werewolf may look ugly (not wolf like), but he is inspired by real illness which people had. So, this is the most realistic looking possible. Full moon, transformations, roaring and killing people, it all inspired later werewolf movies.
3. Frankenstein - Proof that God is not only who can bring life (crazy scientists can too, but cannot create soul anyway). And human's creation from several corpses made Frankenstein. Actually it got name from it's creator, Dr. Frankenstein, it was famous just as ,,Monster". Anyway, basically ,,tank monster", just brute strength and limited intelligence and is wild (because he has brain from killer). There are too many versions of Frankenstein even today. And not to forget about Bride of Frankenstein, popular as well.
4. The Mummy - Immothep is here resurrected. As old and ,,main" mummy he has plenty of powers and abilities at his disposal because of curse throwed at him. All mummy movies later are inspired by this one with exotic ancient and mystic Egypt, deserts which associate with mummies.
5. Gillman (Creature from black lagoon) - This is one tropical water themed monster. Humanoid fish looking, powerful, swims and dives deeply, it can terrorize coasts and waters.
6. The Invisible Man - Crazy scientist who found way to make himself completely invisible to eye. He is not monster like rest, but he is definitively dangerous as one or even more. From all Universal classical monsters he has highest score in killings! (he caused train with all wagons to fall from cliff, killing all people inside). Not as strong as others, no fancy abilities, but one cannot see him coming.
7. Phantom from Opera - Honestly I forgot about this one much as I haven't seen him for very long time, but basically dangerous disfigured man, who is actor and masks himself much. And kills.
8. Dr. Jekyll and Mr. Hyde - Another scientist. He created potion so he can split personality. His alter ego, Mr. Hyde looks differently, like ape appearance, and is murder, wild, and fast, strong, agile, can fight with multiple men and escape them, but did not escape single bullet which killed him. Famous character, present in many movies too.
9. Dorian Gray - Lesser famous and present in movies than previous monsters, but still popular. Dorian gray is human whose sold soul or did some magic to bound himself with his own portrait. So his portrait ages instead of him, which means that Dorian is actually immortal, and unlike other monsters, he is pretty actually, and used/abused it to charm women. And he is killer as well. When his portrait got stab, Dorian dies, and exchanges appearance with portrait, so at end, portrait got his pretty face, and his corpse got old disfigured face.
10. The Wicked Witch - This wicked with came from Wizard of Oz. Her iconic appearance and behavior made her one of main symbols for witches. Green face, black suit and hat, and broom... We saw this in many movies so far and is common for Halloween costumes for girls. She has plenty of abilities as well.
11. Professor Edward C. Burke or The Man in the Beaver Hat - This is special case. This character came from ,,London after Midnight" movie which was lost. It was silent movie, before those Universal classics. This character is tricky as professor ,,The Hypnotist" actually hired actor to play this character as vampire so he can find real murderer in movie. So technically he is not monster, but he inspired many other evil characters until today with this unique scary appearance (scary face, long hat and lamp), so we saw similar characters as grave robbers/diggers and others.
12. Nosferatu/Count Orlok - This is exception, as Dracula belonging to vampire already exists. But this Count in movie is made before Dracula himself and is different, which also made symbol for this type of vampire with different appearance. Unlike Dracula who is in elegant suit with some abilities, Nosferatu actually is hairless and has long fingers and nails, and has two sharp teeths like bat itself. Also, another main difference from Dracula is that Count Orlok brings himself plague in surrounding area, so people shortly start massively dying because of unknown disease.
Here you got with short brief. Now lets hear from you, your opinion, I will put mine soon.