Jonathan David Haidt is an American social psychologist and author.

Niccolò di Bernardo dei Machiavelli was a Florentine diplomat, author, philosopher, and historian who lived during the Italian Renaissance.

Friedrich Wilhelm Nietzsche was a German philosopher and writer who started his career as a classical philologist and turned to philosophy early in his academic career.

Aldous Leonard Huxley was an English writer and philosopher.

Miguel Ángel Ruiz Macías, better known as Don Miguel Ruiz, is a Mexican author of Toltec spiritual and personal development texts..

Viktor E. Frankl (March 26, 1905 – September 2, 1997) was an Austrian psychiatrist and psychotherapist born in Vienna, Austria. He developed logotherapy, known as the "Third Viennese School of Psychotherapy," a psychological approach centered on the importance of meaning in life. He is best known as the author of *Man's Search for Meaning*, a first-hand account of his experiences in Nazi concentration camps.