If i'm a Scorpio rising but my lord of geniture is Jupiter, am I ruled by Mars or by Jupiter?
First of all, I recommend Demetra George's book¹, where she goes into depth about all these different types of Hellenistic "lords" and "masters".
The ruler of the Ascendant and the first house signifies the person, it's more likely to point to things related to health, appearance, temperament, mind and life focus. Its placement, its relationship to the rest of the chart and aspects will point to where and how the native will find themselves frequently in their life, with those things being very central or defining of their personal narrative. If you have a planet conjunct your ascendant ruler or a very close aspect it could represent another person who's always there in your life, or some thing that's more present in your story than anything else.
But the ascendant ruler is not necessarily the strongest planet in your chart. Sometimes the native will have a 10th house ruler that's a lot stronger; and this could cause, let's say, the personal to be less imperative than the professional. But this doesn't mean that the 10th house ruler won't mean anything about who you are.
Throughout the history of astrology, all authors disagreed on the correct way to elect the most influential or most important planet in a nativity. "Lord of the Geniture" is what William Lilly (17th century England) called his own version of it while offering his point of view on that concept. Here's what he said:
I am cleerly of this opinion, viz. That Planet who hath most essentiall and accidentall dignities in the Figure, and is posited best, and elevated most in the Scheame, that he ought to be Lord of the geniture, and am confident the whole actions of the Native will more or lesse pertake of the nature of that Planet and so his Conditions, Complexion, Temperament and Manners shall be much regulated unto the properties assigned that Planet (consideratis, considerandis;) yet doubtlesse if any other Planet be very neer so strong as him whom we formerly mentioned, he shall much participate, and a kind of mixture must be framed according to the severall fortitudes each Planet hath, together with the aspects good or evill of the other Planets intervening.²
Well, here he says the lord of geniture will also have to do with someone's actions, conditions, complexion, temperament and manners, all things we normally assign to the ascendant ruler. That's where it becomes a philosophical problem because astrology is older than our contemporary idea of identity or the individual. Our contemporary ontological theory is that you are your interiority, or your brain, or your mental illnesses, or your mannerisms, your manias, you're just interacting with the world as a removed being; but the astrological chart is about all of your life and everything that happens in it and those things form character. Astrology studies fate and your fate isn't removed from who you are. That's possibly some of what Heraclitus means by "ethos anthropos daimon". ³
Although it's important to be clear that I'm talking about an ontological theory where destiny/fate is involved, but the astrological chart itself isn't you at all, of course, because it's just an oracle, a symbolic tool that helps understand life. My point here is NOT to have you identify with your chart and think that all the planets in a chart have profound subjective meaning. The ruler of the ascendant is symbolic of you, yet the Lord of Geniture can also signify things about you and those things may feel and actually are very personal, because it's your life.
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¹ The book is "Ancient Astrology in Theory and Practice: A Manual of Traditional Techniques, Volume II: Delineating Planetary Meaning". It's all of the Part Nine, but Lilly's Lord of Geniture is more similar to the ancient Lord of the Nativity (Kurios) which she talks about in chapter 94. If you can't find that book you can talk to me through chat and I'll help.
² William Lilly - Christian Astrology, book 3 chapter CV Of the Lord of Geniture. If you go there to the chapter, you'll possibly notice that in the paragraph that I cut out from the citation he mixes the Kurios with the Oikodespotes. Those different versions from other authors that he's rejecting were different concepts entirely.
³ See "The Daimon in Hellenistic Astrology: Origins and Influence" by Dorian Greenbaum.
