This thesis will focus on the problem of the fantasy of self-mastery by comparing Poe’s “William Wilson” with The Horned Man, a recent novel written by James Lasdun in 2002. In studying the fantasy of self-mastery in these two texts, I intend to hold a reconsideration of the Enlightenment concept of the individual. By Lacanian reading of the Double motif in “William Wilson”, I locate the fantasy of self-mastery in the pursuit of self-unity. In Lacanian terms, self-unity comes from the subject’s identification with mirror reflection that creates the sense of mastery. However, by inducing the subject’s identification, the obsession with the unified self will also send the subject to a fantasy of self-mastery. As the tale presents the obsession with a unified self as suicidal in the end, I thus consider the tale as forming a critique to the making of the individual regulated by the Enlightenment concept. I also read an anticipation of the involuntary condition of post-modern subject in the tale. Studying the same employment of the Double motif in the novel, I find its unique accentuation of the rationalist style can be able to push further the critique formed in Poe’s tale. I see the rationalist attitude as where the fantasy of self-mastery expresses itself. From the novel’s detective narrative, I discover that under the rationalist surface lies actually a denial of the irrational self. By employing Terry Castle’s critique of the Enlightenment rationalism to read such self-denial, a process of alienation within the subject can be represented. In The end, I argue that through such self-alienation, the power of self-regulation can be internalized within the subject, who is in turn subjugated by social institutions and ideology.