S tephen Mandel Jr. is an American billionaire investor and the founder of the hedge fund Lone Pine Capital. He is a prominent 'Tiger Cub', a term used to describe the many successful hedge fund managers who honed their craft while working for the legendary investor Julian Robertson at his seminal firm, Tiger Management. Before joining Tiger, Mandel worked as a mass-market retail analyst, an expertise he would leverage throughout his career.

In 1997, he founded his own long/short equity hedge fund, Lone Pine Capital, naming it after a pine tree at his alma mater, Dartmouth College, that famously survived a lightning strike. Lone Pine became one of the most successful and respected hedge funds in the world, known for its deep, fundamental research and its long-term investment horizon. After decades of generating exceptional returns for his investors, Mandel announced his retirement from managing the firm's funds in 2019 to focus on his extensive philanthropic activities through his Zoom Foundation, which is a major supporter of educational and environmental causes.