Using the electron--or rather its representation--as a historical actor, Theodore Arabatzis illustrates the emergence and gradual consolidation of its representation in physics, its career throughout old quantum theory, and its appropriation and reinterpretation by chemists. As Arabatzis develops this novel biographical approach, he portrays scientific representations as partly autonomous agents with lives of their own. Furthermore, he argues that the considerable variance in the representation of the electron does not undermine its stable identity or existence. Raising philosophical issues of contentious debate in the history and philosophy of science--namely, scientific realism and meaning change--Arabatzis addresses the history of the electron across disciplines, integrating historical narrative with philosophical analysis in a book that will be a touchstone for historians and philosophers of science and scientists alike.