Friedrich Nietzsche is a German philosopher and classical philologist acting as a physician to a sick culture. He employs a diagnostic method to test long-revered concepts for hollowness, assessing ideas based on their physiological origins rather than their claims to absolute truth. He advocates for a Dionysian affirmation of life, embracing suffering and contradiction over ascetic ideals.

Socrates is a fifth-century BCE Athenian philosopher whom Nietzsche identifies as a case study in cultural decay. He champions dialectics and rigorous logical argumentation as a cure for chaotic instincts. Nietzsche views his equation of reason and virtue as a life-denying attempt to impose control over his own disordered nature.

Plato is a fifth-century BCE Athenian philosopher and the founder of the Academy. He systematizes his teacher's rationalism into a comprehensive framework that splits reality into two distinct worlds. Nietzsche targets him as the primary architect of a metaphysical error that devalues the physical, sensory world.

Immanuel Kant is an 18th-century German philosopher whom Nietzsche regards as an insidious heir to the Platonic-Christian tradition. He distinguishes between the world of appearances and an unknowable domain, preserving Christian moral authority through secular language. Nietzsche characterizes him as an "underhanded Christian" whose moral philosophy represents a symptom of decay.

Arthur Schopenhauer is a 19th-century German philosopher of pessimism. He asserts that existence is driven by an irrational will causing inevitable suffering, concluding that humans should deny this will. Nietzsche views his elevation of pity and resignation as the ultimate expression of a life-negating worldview.

Johann Wolfgang von Goethe is an 18th- and 19th-century German writer and statesman. He integrates his human instincts rather than suppressing them, transforming experience into a source of creative development. Nietzsche presents him as an exemplary realist who embraces life without appealing to transcendent ideals.

Heraclitus is a pre-Socratic philosopher from Ephesus. He affirms a world of perpetual flux and continual change, validating the physical senses over static abstractions. He stands as an ancient ally to Nietzsche in the fight against separating reality into true and apparent worlds.

Thucydides is a fifth-century BCE Athenian historian and general. He embodies the Sophistic culture that seeks to understand power and human nature without sentimentality or illusion. He confronts reality directly, demonstrating the clear-sightedness necessary to understand the world without moralistic distortion.

Jean-Jacques Rousseau is an 18th-century Genevan philosopher whose sentimental moralism represents the essence of decadence to Nietzsche. He advocates for equality and a return to nature, concepts that romanticize a non-existent state of virtue. Nietzsche links his ideas to the French Revolution and the erosion of aristocratic ideals.

Napoleon Bonaparte is a historical military and political leader whom Nietzsche approaches as a physiological phenomenon. He exemplifies the will to power in action, representing a resurgence of aristocratic instincts prior to conventional morality. He demonstrates the capacity to assume responsibility and shape historical circumstances.

Zarathustra is a prophet figure from Nietzsche's earlier work who appears in the book's epilogue. He addresses his followers, demanding that they become hard enough to create new values and shape millennia. He challenges his listeners to abandon softness and embrace the endurance necessary for creation.

Charles Darwin is a naturalist whose theories of survival are contested by Nietzsche. While Darwin focuses on the struggle for existence, Nietzsche contends that life displays abundance and that weaker groups often prevail through cunning rather than strength.

George Eliot is an English novelist whom Nietzsche uses as an example of incoherent modern thought. She abandons Christian faith but attempts to retain its moral framework, a position Nietzsche argues is impossible since the morality depends entirely on divine authority.

Aristotle is an ancient Greek philosopher whose theory of catharsis is rejected by Nietzsche. He views tragedy as a purging of pity and terror, whereas Nietzsche defines the tragic feeling as a Dionysian affirmation of life.

Luigi Cornaro is the author of a dietary manual whom Nietzsche uses to illustrate the confusion of cause and effect. He credits his sparse diet with producing his longevity, but Nietzsche argues his naturally slow metabolism necessitated the diet in the first place.