When you buy a car from its original owner, you know it's only been owned by one person. Original means "the very first."
Original comes from the Latin word originem, which means "beginning or birth." Whether you're using it as an adjective to describe something that is literally the very first, or as a noun meaning something that serves as a model for making copies, original means "first." Even when you describe an original idea, meaning "something fresh or unusual," you're talking about the first idea of its kind.