Objectivism is a philosophical system developed by Russian-American writer Ayn Rand. Rand first expressed Objectivism in her fiction, most notably The Fountainhead (1943) and Atlas Shrugged (1957), and later in non-fiction essays and books. Leonard Peikoff, a professional philosopher and Rand's designated intellectual heir, later gave it a more formal structure. Rand described Objectivism as "the concept of man as a heroic being, with his own happiness as the moral purpose of his life, with productive achievement as his noblest activity, and reason as his only absolute". Peikoff characterizes Objectivism as a "closed system" insofar as its "fundamental principles" were set out by Rand and are not subject to change. However, he stated that "new implications, applications and integrations can always be discovered".