Peter Singer is an Australian philosopher, author, and Princeton University Professor of Bioethics. He is sometimes described as “the most important living philosopher” and is best known for his book Animal Liberation, widely regarded as the touchstone of the animal liberation movement. He has also written extensively on topics of applied ethics, including abortion, euthanasia, world poverty, and anthropocentrism. 
"We have no need to postulate gods who hand down commandments to us because we understand ethics as a natural phenomenon." 
In a debate with Christian, Dinesh D'Souza, Singer states: "Now, when we're talking about God, of course, that concept can mean a lot of different things to a lot of different people. Since this is a Christian institution, since I know Dinesh D'Souza is a Christian, and since we are living in a society that is Christian in its culture, I am essentially going to talk about the Christian or the Judeo-Christian conception of God. And that's the being which I think I can claim does not exist....But of the Christian, the Judeo-Christian God, I think we can be clear that that being does not exist. And the reason we can be clear about that is by looking at the world around us."