In ethology (the study of behavior), the term alpha male refers the dominant male member among a group of social animals. The term assigns the first character of the Greek alphabet (alpha) to the position of the most dominant member of the hierarchy.
War has customarily been viewed as being for men in another sense too: as an occupation and destiny which not only differentiates them from women, but also enables stronger, braver, alpha males to distinguish themselves from less impressive specimens of their own sex.
— Linda Colley, The New York Review of Books, 13 May 2004
Following the analogy of the alphabet, beta animals are often the second most dominant members, becoming more aggressive when the alpha is absent, while omega animals tend to be the most submissive of the group.