Wikipedia is a large and rapidly growing Web-based collaborative authoring environment, where anyone on the Internet can create, modify, and delete pages about encyclopedic topics. A remarkable property of some Wikipedia pages is that they are written by up to thousands of authors who may have contradicting opinions. We define a network of authors revising other authors and present methods for its visual analysis that yield interesting insight into the structures of controversy by highlighting the dominant authors of a page, the roles they play, and the alters they confront.