Here are just a few names of people who have contributed to our better understanding of happiness. The list is far from complete, but it is a place to start.
In alphabetical order:
Al-Ghazali
Aristotle
Thomas Aquinas
Tal Ben-Shahar
Buddha
Neil Cohn
Confucius
Mihaly Csikszentmihalyi
Richard Davidson
Ed Diener
Carol Dweck
Barbara Ehrenreich
Epicurus
Victor Frankl
Barbara Fredrickson
Marie Jahoda
William James
Jonathan Kabat-Zinn
Danniel Kanneman
Dacher Keltner
Ellen Langer
John Locke
Sonja Lyubomirsky
Abraham Maslow
Iris Mauss
Mencius
Robert Novick
Shigehiro Oishi
Mathieu Ricard
Laurie Santos
Martin E. Seligman
Emiliana Simon-Thomas
Socrates
Dr. Amit Sood
William Tov
Ashley Whillans
Zhuangzi
( Additionally, https://www.pursuit-of-happiness.org/ offers detailed discussions about many key figures in happiness research.)
Happiness and Culture 