This thesis argues that there is an enigma at the heart of Webster's The Duchess of Malfi; a disjunction between the critical history of the play and its reception in performance. Historical disquiet about the status of the play among academics and cultural commentators has not prevented its popularity with audiences. It has, however, affected some of the staging decisions made by theatre companies mounting productions. Allied to other practical factors, these have impacted significantly – and occasionally disastrously – upon performances. It is argued that Webster conceived the play as a meditation on degree and, in aiming to draw out the maximum relevance from the social satire, deliberately created the multi-faceted performative role of Bosola to work his audience in a complex and subversive manner. The role's purpose was determined in response to the structural discontinuity imposed upon the play by the physical realities of staging within the Blackfriars' auditorium. But Webster also needed an agent to serve the plot's development and, in creating the role he also invented a character, developed way beyond the material of his sources. This character proved as trapped as any other in the play by the consequences of his own moral choices. Hovering between role and character, Webster's creation remains liminally poised on ‘the dangerous edge of things.' Part One explores the contexts in which Webster created one of the most ambiguous figures in early modern drama - subverting stock malcontent, villain and revenger - and speculates on the importance of the actor, John Lowin in its genesis. It includes a subsequent performance history of the role. Part Two presents the detailed analysis of a range of professional performances from the past four decades, attempting to demonstrate how the meaning of the play has been altered by decisions made regarding the part of Bosola.