Alucard
Alucard is Dracula spelled backwards for those who didn't know. Alucard is half Human half Vampire. His mother was Lisa and his father is/was Count Dracula and he is the only vampire who helps humans. 400 years before this game he helped another Belmont kill Dracula. He went into an eternal slumber to purge his bloodline but he had to come out of it since Shaft summoned Dracula so he could kill Dracula for the final time.
Lisa
Lisa is Alucard's mother. She was sentenced to death by an angry mob for supposedly practicing witchcraft. Alucard watched her die, and her last words were, "Do not hate Humans. If you cannot live with them, do not harm them, for theirs is already a hard lot." Dracula didn't here them, so he was enraged and hated humans and wanted to kill them all.
Dracula
Dracula is the strongest among vampires, and returns every century. He fell in love with a human, Lisa, and was enraged by her death he then decided to destroy the human race. He is defeated by Richter in the begining, but is then resurrected by Shaft in the reverse castle a few years later.
Richter Belmont
Richter is the strongest among all vampire hunters. He is minipulated by Shaft into being lord of the castle and the only way to goto the reverse castle(or free Richter even) is to break the spell that he is under.
Maria
Maria apparantly likes Richter. She gives Alucard the glasses needed to see the orb that is holding Richter under a spell so Alucard could destroy it and free him. She helps take Richter to safety after Alucard frees him from Shaft's curse. She also goes after Alucard in the end(depending on how much of the game you completed).
Death
A good friend of Count Dracula, he tries to get Alucard to stop helping Humans and destroy them instead. Since Alucard refuses Death strips him of all his equipment at the beginning of the game. You fight Death later and kill him(if that's even possible).
