Simon Sinek is a British-American author and motivational speaker best known for popularizing the concept of the Golden Circle — a framework built around three concentric layers: Why (purpose/belief), How (process/values), and What (product/service). His central thesis is that inspired leaders and organizations start with WHY they do what they do, rather than leading with what they do or how they do it. This idea drew from ethnographer Terence McNahan's concept that people don't buy what you do, they buy why you do it.
His 2009 book Start With Why: How Great Leaders Inspire Everyone to Take Action laid the foundation for this philosophy and became a business classic. His TEDx talk "How Great Leaders Inspire Action" (delivered at TEDxPugetSound, later reposted to the main TED platform) became the third most-watched talk on TED.com with over 50 million views. In it he analyzed why companies like Apple, Martin Luther King Jr., and the Wright brothers succeeded at inspiring action where others failed.
Sinek subsequently authored Leaders Eat Last: Why Some Teams Pull Together and Others Don't (2014), which explores the biology of leadership and why great leaders create circles of safety that enable collaboration and risk-taking. He also wrote The Infinite Game (2019), applying similar thinking to long-term strategic vision versus short-term competition. His work is frequently cited in Silicon Valley, military leadership, and education circles.