This essay explores the roots of the concept of "Cainism" in Spain's history, investigating the influence of the biblical figure of Cain in Spanish literature. It is divided into two parts: the first examines Cain's portrayal in the Bible and its literary evolution, while the second focuses on how Cain's figure was used in Spanish historical narratives to justify the disdain for other religious communities and explain fratricides. The work highlights the impact of the Hebrew Bible on Spain's historical narrative.