The 2008 TIME 100

I met Mehmet Oz at a luncheon in 2004 and had no idea who he was—a fact that even then put me in a minority. The Columbia University heart surgeon, 47, who now has a series of best-selling health books and a forthcoming TV show, was already a famous face. As we talked, it became clear that I was as intrigued by his work in the hospital as he was by mine in the kitchen of Le Bernardin, so we agreed to try out each other's job.

For two days, I went to the OR with Mehmet, followed him on his rounds and even tried operating on a pig heart. I thought I did well but later learned that if the heart had belonged to a human, the patient would have died. Mehmet did a lot better in my world than I did in his. He immediately took charge of my kitchen, was completely at ease leading my team of 40 cooks and even took time to greet guests. But it was not when he was interacting with diners and cooks that I learned the most about him; it was when he was interacting with patients. He is a man of extraordinary compassion and strength, remarkably suited both to caring for his own patients and to carrying a message of health to a larger world. Perhaps when you've had the powerful experience of opening human hearts, you find it a little easier to open your own.

Ripert is executive chef and co-owner of Le Bernardin in New York City