Once my freshman year of college. This athlete would follow me to my dorm late at night, to events I went to, and call me in the wee hours of the morning. After Christmas break, it seemed to clear up on it's own.
Second time, I moved away from an ex. He found me and took a job in the new city I moved to. He made online accounts pretending to be different people to talk to me etc. After a year, he left me alone.
All things considered, I feel very fortunate to not have had anything really bad happen to me.