It's important to note that:
* Defining "individualism" broadly: There are countless books that touch upon individualism, even if it isn't the central theme.
* Authorship: Some authors might have written over 100 books overall, but only a small percentage might directly explore individualism.
* Collaboration: Many books are collaborative efforts, making it difficult to attribute specific themes to one individual author.
Potential candidates for authors who have explored individualism extensively in their work:
* Ralph Waldo Emerson: A prominent transcendentalist who emphasized self-reliance and individual intuition.
* Henry David Thoreau: His work, particularly "Walden," explores the importance of self-sufficiency and living in harmony with nature.
* Ayn Rand: Her philosophy of Objectivism promoted rational self-interest and individual achievement.
* Alexis de Tocqueville: His observations of American society in "Democracy in America" focused on the role of individualism in shaping American culture and politics.
Rather than focusing on a specific author with over 100 books, it might be more insightful to explore the diverse literary landscape that has grappled with the complexities of individualism in American society.