Stalker (noun)

A person who harasses another person by following or contacting them repeatedly.

Origin:

From the verb stalk, which comes from middle english stalker, from old english bestealcian "to go stealthily".

Examples:

1. She had a restraining order against her ex-boyfriend, who had been stalking her for months.
2. He was arrested for stalking after repeatedly showing up at her workplace.
3. The stalker was persistent in trying to contact her even after she blocked his number.
4. The police warned her to be careful, as the stalker seemed to be escalating his behavior.
5. She was being stalked by an unknown person and was feeling very unsafe.