Ray Kroc didn't start McDonald's (MCD), but he recognized a winner when he saw one. Kroc was a paper cup and milkshake machine salesman who was so impressed by the McDonald brothers' restaurant he called upon one day, that he dropped everything (much to the dismay of his risk-averse wife, who thus got dropped in turn) to build the company more or less into what it is today. He shares his story in his book Grinding It Out.
Kroc is one of those guys who shows that you're never too old to be an entrepreneur. He was 52 when he started his McDonald's gig, and he kept at it for another 20 years as the company took the country by storm.
Kroc's stint can be characterized by a massive expansionary policy (he would have fit right in at today's Federal Reserve!) and a relentless focus on process. For example, he spent a great deal of time making sure the fries in his first new Macdonald's tasted exactly as they did in the original store. He established an R&D department and a training school for franchisees. Both of these may be considered the norm/essential for franchisors today, but back in the 1960's this was innovative stuff.
Usually, I'm bored stiff when entrepreneurs discuss their personal lives: we get it, you couldn't have done shit without the support of your wife. But Kroc's story is rather fascinating. His first wife just wasn't supportive enough of his business endeavours, so that didn't work out. His third wife was someone he propositioned while she was still married to her previous husband, a McDonald's franchisee! Kroc makes no apologies for this behaviour, his attitude being: when it's right it's right.