The chart ruler is the planet that rules your Ascendant, which governs the role that you play in life and the general script you write for your life. I’ve written another post on the chart ruler which you can check out here: http://astroarena12.blogspot.com/2015/03/the-chart-ruler-what-kind-of-movie-is.html
So, what happens when the chart ruler is in the transcendent, egoless 12th House? What’s your role, then? Well, this actually means that you are supposed to stretch yourself far beyond the role of your Ascendant and its ruling planet. It’s a confusing thing (of course it is; it’s the 12th House!) and it can take a long time for the person to realize that the old role must be released. You have to kind of give up your Ascendant when the chart ruler’s in the 12th. At least, you give up claiming it for yourself; for your ego. You have to surrender and be willing to not necessarily be this planet in an individual way but help your fellow human beings find their way toward this planet.
The 12th House is about the collective. It’s humanity. It’s not about our little egos. That’s what the 1st House and the Ascendant is. It says, “Here I am! This is me!” But, the 12th House cannot say, “This is me!” because that’s ego. It must say, “This is all of us.” Therefore, when your chart ruler is in the 12th, you must come to realize that you cannot claim that planet’s energy for yourself. When you do, there are not only karmic consequences but a terribly overwhelming feeling that comes with it. Your 12th House chart ruler must, in many ways, be surrendered while still acknowledged.
Therefore, you’ll stop seeming like a traditional example of that Rising sign. People might not be able to clearly see that energy in you or pin it down. But, there’s still a part of you that is very attuned to the chart ruler’s energy and you’re here to allow other people to be more attuned to it within themselves. You can draw others back into the tapestry of the collective by guiding them toward your chart ruler’s principles. So, this gives off the subtle impression that you are this energy. But, at the same time, it being in the elusive 12th House doesn’t make itself known too much.
Let's say that you're a Capricorn Rising with Saturn in the 12th. Your life will be more about showing people their inner Saturn: helping them be accountable for themselves, showing them how they can command their destinies, directing them toward a more important purpose. And because of being interested in such wisdoms, there’s still something “wise old-soul” about you. If you have a 12th House Mercury as the chart ruler, you’re not supposed to seek recognition for being intelligent and communicative. You’re supposed to help humanity be more intelligent and communicative, which in the end still gives you a rather smart aura. If Pluto in the 12th is ruling your chart, show your fellow human beings how they’re powerful, instead of trying to gain power for yourself. But, that, in and of itself, is a very powerful thing.
When it comes to yourself, that chart ruler in the 12th is supposed to be a way to recharge your batteries and withdraw. It’s made for your inner world. It's not supposed to be established fully in the outer world. It’s probably even a powerful source of your art, your fantasies, and your dreams. This is how it’s experienced; in an unworldly fashion. It might take a lot of suffering for you to realize that you just cannot express your Rising sign in a ways that serve the self and the ego; that’ll make people say, “You’re a Scorpio Rising, aren’t you?” Through this realization and this state of surrender, you find that 12th House redemption. This is true even if your chart ruler in the 12th happens to be conjunct your Ascendant, as I think 12th House planets rising are much different than 1st House planets rising. They’re meant to be very internalized and private.
You can see this in many celebrities who have/had their chart ruler in the 12th. Heath Ledger was not your typical Aries Rising. He was shy, reserved, kept to himself. And his chart ruler, Mars, was in the 12th. Yet, look closely and you still see a smoldering inner Martian fire beneath that shyness that made him the force of nature that he was in the acting world. Meryl Streep makes for quite a low-key, self-effacing Leo Rising. Her chart ruler is the Sun and it’s in the 12th. But, beneath the surface of that unshowy demeanor is a powerful glow, a dignity, and a light that screams Leo. Yet, like Heath’s energy, it’s very subliminal and seems to elude you as soon as you see it.
If the chart ruler determines what kind of life you have, then having your chart ruler in the 12th means living a life of being unknowable or incomprehensible, in some manner. And if the Rising sign gives other people an immediate impression of who you are, then having a 12th House planet ruling your chart means that their immediate impression is, “Who are you? Cause I’m not really sure.”