Here are four core arguments against God's existence that have persisted since ancient times. Using these four arguments as an organizing principle, I present for your consideration the Four Horsemen of 1934-1988. Kurt Vonnegut (1922-2007) also deserves mention as a contemporary of these authors as well as the Four Horsemen.
The argument from evil- If the gods are real, they have a lot of explaining to do. Richard Feynman addressed the problem of evil with a universe without a unifying purpose.
Lack of empirical evidence- Discovery trumps revelation. This is the skeptical or naturalistic argument. As Madalyn Murray O'Hair observed, religion cannot be reconciled with science.
The argument from reasonable nonbelief- If the existence of the gods were self-evident, everyone would believe. The burden of proof is on religion. As Carl Sagan observed, obstinate faith is wishful thinking.
The Four Horsemen that we know today are very much a product of their time. They are identified with the attacks of 9-11, but their influence is due in no small part to their recency in history. They represent the ongoing struggle of the Enlightenment at the present moment. Their historical context sets them apart and makes any comparison seem tenuous.
More important than designating any particular four horsemen of any particular generation is the observation that since the Enlightenment, there has been no shortage of prominent antitheists. At least four can be identified at any moment. The original Four Horsemen have distinguished themselves for their tenacity. Not only do they insist that unreason deserves no refuge--as others have done before--they have consistently refused it hospitality and inspired others to follow suit.