Won't take no for an answer
Has an obsessive personality
Above average intelligence
Low self esteem
Has a mean streak
Lack of embarrassment or discomfort at actions
No or few personal relationships
Reality: I had a stalker a few years while I lived in California in the 80s. It was before they had laws about such harassment. The cops came and talked to me and basically told me they knew the guy had done the same thing before and all they knew was that he drove a van. It is sad that there are people who so few connections with human beings that they have to glom onto someone and hope to find some satisfaction in a fantasy world with that object of their obsession. They obviously missed some important steps in the interactions with others in which the person they interact with returns the attention and affection. Those broken tendrils in one's psyche--they lead to some horrifying scenarios. Just look at these few movies about stalkers and realize there are hundreds more out there about the subject that is classified as "horror."