When Saeju Jeong moved from South Korea to the U.S. in his mid-20’s, he barely knew anyone, didn’t speak much English, and had only $5,000 in savings. Today, he’s the CEO of Noom, one of the most popular weight loss/wellness apps in the U.S. Inspired by his late father—a doctor who criticized the profession for treating people only after they got sick—Saeju and his co-founder built their first fitness product in 2007. Several pivots later, they arrived at Noom, an app that carefully tracks what you eat, how you sleep and when you’re stressed out. Noom has hinted it may go public this year—if so, the valuation could be as high as $10 billion.