Which philosopher originally proposed having "aims" or "intentions" as a condition of (moral) personhood?
I often see this used in discussions of abortion and euthanasia: e.g., "He does not have aims, therefore, he is not a person..."
Your question is vague, only insofar as contemporary explanations of philosophy tend not to be concerned with priority of ideas (as in who came up with what first, though there are exceptions and the inverse is a valid method of teaching philosophy). Rather, philosophical concepts tend to be taught as related to those who formulated them the best, where the best is understood as fulfilling a given pedagogical model.
In regards to your question, then, in ethics, a broad distinction is often made between a body of arguments sometimes called consequentialism, and a body of arguments sometimes called intentionalism. The difference, of course, being one of emphasis - the former argues, generally, that the outcome or consequence of an action is the substance of ethical debate, whereas the latter argues, generally, that the intention or motive of an action is the substance of ethical debate. Famous figures: John Stuart Mill is associated with the former, Immanuel Kant with the latter (though this black and white distinction does injustice to the complexity of their thought, as well as other ways of grouping ethical debates).
There have been many historical formulations of intentionalism and consequentialism under different names, and involving radically different concepts. If what you are looking for is the progenitor of the idea that intention matters most in ethics, then this is a very difficult question to answer with accuracy. Socrates held the view that it is better to suffer injustice than to do injustice because doing injustice damages the soul. One could construe this (if one were inclined) to mean that motives matter more than outcomes, because internal states are more important than external conditions.
The situation is sticky because ethics is not a closed branch of thought, but is actively pursued by philosophers alongside other considerations (such as metaphysical and epistemological ones), the outcomes and methods of which affect their response to ethics. Furthermore, historically, ethics has meant different things to different people. Generally, for example, for the ancient Greeks, ethics was a discussion of how to live a good life - whereas modern considerations tend to avoid instructions and arguments for living well and instead tend toward arguments concerning how a person ought to treat others.
Now, if I were to take a wild stab at the famous name most likely associated with contemporary debates about intention vs. consequence, I'd say it's Kant. Though, he is more often lumped under a conceptual category in ethics called Deontology.
In addition to being the argument of the famous paper by Giublini and Minerva (2012) on after-birth abortion, this seems to be Boonin's argument in his Defense of Abortion (2002), particularly if we may replace "aims" with "desires" and "personhood" with "right to life." This paper (Beckwith '06) summarizes the relevant argument thus:
a. Organized cortical brain activity must be present in order for a being to be capable of conscious experience,
b. Prior to having a conscious experience, a being has no desires,
c. Desires (as understood in Boonin’s taxonomy; see below) are necessary in order for a being to have a right to life,
d. The fetus acquires organized cortical brain activity between 25 and 32 weeks gestation,
e. Therefore, the fetus has no right life prior to organized cortical brain activity.
Like other contemporary philosophers,13 Boonin maintains that rights depend on desires.
The footnote mentions Dworkin as an earlier source of this argument. Dworkin comes closer to describing "aims":
13 For example, Ronald Dworkin argues that [...] "Having rights seems to presuppose having interests, which in turn seems to presuppose having wants, hopes, fears, likes and dislikes. But an early fetus lacks the physical constitution required for such psychological states.” Ronald Dworkin, Life’s Dominion: An Argument About Abortion, Euthanasia, and Individual Freedom (New York NY: Vintage Books, 1994), p. 15.
Boonin goes on to develop the idea of "desires," distinguishing between "dispositional" and "occurrent" desires and "real" and "actual" desires. These distinctions seem to broaden the idea of "desires" to include something like what we might call "aims":
According to Boonin, “a desire of yours is occurrent if it is one you are conspicuously entertaining,” such as your desire to read the rest of this sentence. On other hand, “a desire of yours is dispositional if it is a desire that you do have right now even if you are not thinking about it at just this moment,” such as your desire to live a good long life (p. 122).Thus, according to Boonin, all things being equal, it seems reasonable to attribute to the temporarily comatose adult certain dispositional desires including a desire to not be killed. So, according to Boonin, it is dispositional desires that ground one’s right to life, for one has a right to life even if one is not presently aware of desiring it. But what about people who have occurrent and/or dispositional desires for perceived goods that are inconsistent with what they would desire in the future? For example, a person may have the desire to engage in an act that deprives her of life because she is depressed, holds false beliefs, or has acquired incomplete information. In order to address this problem, Boonin introduces a distinction between ideal and actual desires. To employ one of Boonin’s own examples: although you may have an actual occurrent desire to drink a glass of water that you do notknow is laced with poison, “we may confidently consider your ideal desire to avoid drinking from the glass, given that your actual (though likely dispositional rather than occurrent) desire not to be killed strongly outweighs your actual (even if occurrent) desire to quench your thirst”(pp. 123-24).
Writes Boonin, Once an individual does develop such desires, the potential that his brain has for developing further becomes morally relevant: It is because a human infant’s brain has a potential that a mature cow or pig does not have that the human infant uncontroversially has a future-like-ours, whereas the cow or pig does not. And it is because of this that the conscious desire that an infant has provides a solid foundation for attributing to it an ideal dispositional desire that its future-like-ours be preserved, whereas this cannot be said of the conscious desires of the cow or the pig. (p. 126, footnote omitted).
For what it's worth, I also found a minor link between personhood and aims in Dewey's 1916 Democracy and Education.