http://stephenking.wikia.com/wiki/It_(creature)

"It apparently originated from an undiscovered void containing and surrounding the entire Universe, a place referred to in the novel as the "Macroverse" (a concept later established as the Todash Darkness of the Dark Tower Novels). It's real name (if, indeed, It has one) is unknown—although at several points in the novel, It claims its true name to be Robert Gray—and is named "It" by the group of children who later confront It. Throughout the book, It is generally referred to as male; however, late in the book, the protagonists come to believe that It may be female (due to its manifestation as a monstrous female spider). This is, however, not It's "true form," it is simply the closest the human mind can come to approximating it. It's natural form exists in a realm beyond the physical, which It calls the "deadlights" (described as writhing, destructive orange lights). Coming face to face with the deadlights drives any living being instantly insane. Bill comes dangerously close to seeing the deadlights; after looking into It's eyes, he saw the shape behind the shape for a brief moment. He described the sight as an endless, crawling hairy creature made of orange light. But he and Richie successfully defeat It before the deadlights can impact Bill. The only known person to face the deadlights, survive, and regain her sanity is Audra Phillips."