Atheism is the rejection of all currently made god claims. Just like Theism, it is an umbrella category for an incredible variety of different ideologies and moral systems. Just like there is no one leader for Theism -- there are actually leaders of different branches of Theism and there are branches of Theism that are more Congregationalist or Individualist -- the same is true of Atheism.
There are numerous categories of Atheists who add belief systems to create a moral system since the religious moral system is no longer applicable. Some of these groups include:
1) Rationalist Skeptics: The most prominent type of Atheists today are Rationalist Skeptics who believe that empirical results and the scientific method can be used to determine whether something is true or false and that information can be plugged into some sort of utilitarian system in order to determine its morality. These Atheists tend to have a more individualist attitude, but rally around particular individuals who they argue are advocates of the movement. These leaders include, but are not limited to: Richard Dawkins, Christopher Hitchens, Sam Harris, Ayaan Hirsi Ali, Matt Dillahunty, Aron Ra, and Maryam Namazie. Rationalist Skeptics, like most Theists will disagree with these leaders on particular aspects of policy, such as Hitchens's endorsement of the Iraq War, but will generally agree with the world view provided.
2) State-Religionists: Another type of Atheists are the State-Religionists, who believe in the validity of the founding ideals of a state or a political system as being the arbiter of moral justice. State-Religionists are usually termed as "nationalists" or "patriots" and have been behind most of the major democides of the 20th century, the Soviet democide, the Chinese democide, the Cambodian democide, etc. The leaders of State-Religion are usually the leaders of the state, who often have a quasi-divine sheen to them. Stalin, Mao, Ataturk, etc. are the leaders of these State-Religions and the Atheists who follow them allow the morality of these leaders to supersede their own. North Korea's Juche is often considered to be a state-religion which has actually crossed back into a Theistic Faith since it actually deifies Kim Il-Sung and his progeny.
3) Apatheism: Still another type of Atheist is the Apatheist, which is person who does not believe in gods because he or she does not care to investigate the question, seeing it as irrelevant. The largest number of Apatheists are Atheist Buddhists, since the Buddha was himself an Apatheist according to his own writings. Apatheists often have a spiritualist philosophy and will point to a philosopher or theologian in the Eastern tradition (a guru, Buddha, Lao-Tzu, etc.) as their source of ethics or moral principles. Since most of these people are not alive anymore, their leadership is emotional or articulated, not current.
