This introductory chapter provides an overview of gendered characters in debates about autism. Researchers seeking to understand autism have often drawn on gendered characters to theorize what autism is and what causes it. Others seeking to intervene in autism debates, especially parents, have turned to stock characterizations of mothers and fathers for this purpose. Such characters are useful because they can help persuade others to adopt a certain view—a theory of autism, a course of treatment, or a view of the speaker's ethos. This book argues that gaps in scientific knowledge and authority over autism enable gender to become a salient rhetorical force: where knowledge or authority is lacking, gendered characters often fill in. The chapter then describes what autism is, how it has been defined, and how those definitions have shifted over time.