Immanuel Kant's (1724-1825) Categorical Imperative

Kant's Categorical Imperative basically has two tenets:
Act only according to that maxim whereby you can at the same time will that it should become a universal law. See Sartre quote above. Be careful, here, though, because he does not mean "what if everyone drove drunk at the same time?" but rather "what if we always allowed everyone to drive drunk?"

2) Treat other human beings as the ends, not the means to the end.  That is, morality and laws etc. exist to better human beings, and human beings are the purpose for morality and laws;  thus, all moral actions serve to protect -- not use or abuse -- human beings.

The essence of immorality, then, is to make an exception of myself by acting on maxims that I cannot willfully universalize. It is always wrong to act in one way while wishing that everyone else would act otherwise. (The perfect world for a thief would be one in which everyone else always respected private property.)

Kant offered the "formula of the end in itself" as: "Act in such a way that you treat humanity, whether in your own person or in the person of another, always at the same time as an end and never simply as a means." This places more emphasis on the unique value of human life as deserving of our ultimate moral respect and thus proposes a more personal view of morality. In application to particular cases, of course, it yields the same results: violating a perfect duty by making a false promise (or killing myself) would be to treat another person (or myself) merely as a means for getting money (or avoiding pain), and violating an imperfect duty by refusing to offer benevolence (or neglecting my talents) would be a failure to treat another person (or myself) as an end in itself. Thus, the Kantian imperative agrees with the Christian expression of "The Golden Rule" by demanding that we derive from our own self-interest a generalized concern for all human beings.

Drawing everything together, Kant arrived at the "formula of autonomy," under which the decision to act according to a maxim is actually regarded as having made it a universal law. Here the concern with human dignity is combined with the principle of universalizability to produce a conception of the moral law as self-legislated by each for all. As Kant puts it,

'A rational being belongs to the kingdom of ends as a member when he legislates in it universal laws while also being himself subject to these laws. He belongs to it as sovereign, when as legislator he is himself subject to the will of no other.

A rational being must always regard himself as legislator in a kingdom of ends rendered possible by freedom of the will, whether as member or as sovereign.'"