Heinrich Meyer

Heinrich Meyer was a merchant who was turned into a Lizard Man in 1847 after visiting the Castle with the hopes of making a sale. After the transformation, he maintained the ability to speak, but would remain in the Castle. Five years later he was approached by Reinhardt Schneider and Carrie Fernandez, who at first thought he was an enemy. He implored them not to harm him and helped them on their quest.

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From Millenium's Official Castlevania 64 Strategy Guide:
 * Heinrich Meyer, a nearby merchant, visited the castle of Dracula five years agot to ply his trade of wooden artifacts, aware of the presence of evil, but not letting that get in the way of a sale. Once inside the castle, he was offered some tea by a rather pale-looking butler...  Waking up three days later, he discovered to his horror that he was tied to a huge wooden operating bench, and a small mad scientist was working furiously on inserting a number of needles into his arm.  The rest of his body covered in leaeches, Heinrich let out an awful screem and then realized the true terror of his predicament.  A thick rasping noise sounded from his lips...  as he looked down, he saw blue scaled covering his torso and legs.  He was changing... the fearful and quite mad Heinrich (now completely transformed into a lizard man) is kept in a castle bedroom.  He keeps a key for company, and runs from the slightest aggression.