This article explores the royalist libels that afflicted the parliamentarian leader John Pym during the early 1640s to argue that the period marked an important turning point in English libellous politics. First, like many of the political libels circulating in early Civil War England, royalist attacks against Pym transitioned unsteadily from manuscript to cheap print and then finally into official court-sponsored publications throughout the period as contemporaries grew more comfortable with openly libellous language. That medial transformation, in turn, was informed by a broader personalization of politics that drew on early Stuart modes of ‘politic thinking’ to frame the nascent military conflict as a battle of rival political personalities. Both contexts informed the creation and dissemination of the most vicious anti-Pym libel of the period: an allegation that Pym's mother had once committed the act of bestiality with a horse, and that Pym himself was the miscegenated result of their illicit union. Rather than a spurious invention, moreover, the horse libel in fact possessed tangible roots in an embarrassing episode of Pym's family history thirty years prior. Consequently, it demonstrates the importance of oral and scribal transmission alike in shaping and sustaining the vitriolic libellous politics of early Civil War England.