History
The earliest version of natural law theory we know of arguably came from 
Plato, who argued that the various virtues towards which people strive come from the imitable and enteral Form of the Good, which encompassed all other virtues. As such, all humans, once they properly understand the good, seek to find it.
Aristotle is the first uncontested natural law theorist. He thought that the good was a result of human teleology, or the end towards which human beings are oriented.
The 
Stoics divided goods into those which merely came out of the needs of human nature (food, shelter, money) from the goods that must be apparent to any creature capable of reason (the virtues.) Those goods which were merely "in accordance with nature" took a secondary roll to those which dealt with virtue. They taught that all people were capable of reason, and thus, everyone was equal in so far as there ability to use reason.
Aquinas would go on to claim that different goods existed in different ways in different kinds of beings, all of which emanated form the existence of God.
Thomas Hobbes viewed the only prescription of the natural law to be survival, and because you were always better off with a monarch then in a lawless "state of nature", you're monarch could treat you however they wanted.
Around the Time of the 
Enlightenment, 
John Locke introduced the idea of natural rights, claiming that the natural law gave people the right to "Life, Liberty, and the Pursuit of Property." The idea of natural rights has sense become one of the most popular parts of Natural Law Theory.
Beliefs
The Natural Law Theory of ethics makes the claim that there are a variety of goods towards which all of human nature is inclined. Unlike animals or inanimate objects, who are determined by the "laws of nature" we discover through science, humans have the ability to use reason to comprehend the ends towards which they are oriented, and are thus capable of moral or immoral action. Some of the inherent goods given to us by the natural law might be companionship, survival, pleasure, reproduction, or any number of 
virtues.
Relationships
Friends
Moral Universalism - Indeed, morality aplies to all creatures capable of reason.
Virtue Ethics - Were a classic duo!
Aristotelianism - The foundation for most modern natural law theory.
Thomism - Helped to systematize me.
Roman Stoicism - We each helped shape each-others world views.
Classical Liberalism - We both love John Locke.
Conservative Liberalism - One of my biggest supporters in the modern era.
Catholic Theocracy - Same as the last guy, only, even more so.
MLKism - He cited me in "letters to Birmingham Jail."
Anarcho-Capitalism - I hear you're a fan of mine Mr. Rothbard? Wait, what do you mean, parents don't have to take care of there children?
Frenemies
Platonism - Arguably founded me, but now a days, most of my theories are built of off you're students ideas rather then yours.
Cynicism - Look, I appreciate that you're trying to live in accordance with nature, but can you pleas stop masturbating in public?
Hobbesism - I mean... you are a Natural Law Theorist, but you're a pretty unorthodox one.
Hedonism - Pleasure can be good, sure, but isn't there anything else you value?
Enlightenment - I helped shape his world view, but then he ditched me for 
Deontology and 
Utilitarianism.
Conservatism - Why do you only cite me when you're trying to bash gay people?
Lawsonomy - I think you might be a little bit confused about what "Natural Law" actually is.
Enemies
Post-Humanism - Good lord this is horrific!
Anti-Humanism - Okay...but why though?
Nihilism - Oh? And tell me, has lying around all day mopping about how everything is meaningless made you're life any better?
