This is another great question, this time from Lesley. My first thought was to look at the natal chart. However, my second thought was to talk about synastry. There are certain aspects in synastry that can make the most mild mannered among us become a stalker. I exaggerate a bit but I hope you get the point. There are some aspects which make one obsessed. Nessus and Dejanira are classic for obsession. I can go so far as to say that I always see obsession when they are prominent in synastry. Moon/Pluto makes for obsession, as does Venus/Pluto. Remember that orbs are key. Close orbs are much more powerful.
Let’s look at the natal charts because there are some people who are more likely to be stalkers. My first thought would be Pluto. Pluto rules our primal passions. Stalking is about as primal as one can get. Hence, the chart of a stalker would, likely, be very strong in Pluto. Strength of Pluto can be shown in a variety of ways. One is Pluto conjunct the two outer manifesting angles–The Ascendent and the MC. Any native with Pluto conjunct the Ascendent or MC will be a person of power.
Another fascinating Pluto placement is the Unaspected Pluto. This native was born to learn the lesson of wielding power. I am not saying that Putin has an Unaspected Pluto but he would be a classic example of someone who did. I am not saying the Unaspected Pluto will be a stalker. However, he will be compelled to learn how to manipulate power.
A native strong in Scorpio placement would more likely be a stalker. In particular, the Sun, Ascendent, Mercury or Mars in Scorpio because these are more active planets. The passive planets are the Moon and Venus. Hence, the Moon and Venus would be more likely to obsess rather than act.
To be a stalker, one would likely have a strong Mars because Mars shows strength of drive. A weak and impotent Mars, such as Cancer, would not, likely, stalk. The strong Mars signs are Scorpio, Aries and Capricorn. Capricorn would more likely stalk a good business deal. Aries would more likely stalk a good cause, so we have Scorpio.This is my favorite Mars because he is so darn intense when he is in love.
House wise, we would look at the 8th House. Planets residing in the 8th House get repressed. The native with many planets in the 8th is said to mature late. The 8th House can be seen as a pressure cooker because what is repressed has the danger of coming out sideways. Hence, a repressed Pluto could fly out of his cage and who knows what may happen. Venus in the 8th house tends to be very intense when in love. If one has Venus in Scorpio in the 8th house, one can amp the intensity. If one has Pluto conjunct Venus in the 8th house, we have a person who gets totally obsessed when in love, through no fault of his own.
We cannot choose our charts. We can just try to make the best of what we were given.
I know I have omitted many possibilities, as these were just the first ones that came to mind. Tell me what you think and you have experienced. I await your Comments.