When Priscilla Chan began her residency as a pediatrician at San Francisco General Hospital, she warned her attending physician, “I want to tell you up front: I’m a crier.” And cry she did. “When she’s feeling exhausted or overwhelmed, and sometimes when she’s really ecstatic, it’s just one of her ways of expressing,” says Meg McNamara, the doctor who received that warning and has since become a good friend of Chan’s. Today at the Chan Zuckerberg Initiative, where Chan is co-CEO, her tendency to cry is openly acknowledged. She has cried at all-hands staff meetings, at big public gatherings. There are tissues in all the conference rooms, colleagues say, just in case she needs one. She even cried at her first interview for this article, when discussing difficult aspects of her childhood.

Chan, 33, is among the most intriguing emerging leaders around, and not simply because she’s married to Mark Zuckerberg (who most definitely is not a crier). She is a doctor who has become a crusader. And don’t mistake her emotion for weakness. “There was this horrific fire, multiple kids getting burned really badly,” recalls Ryan Padrez, the chief resident who oversaw Chan’s pediatric trauma work at the hospital. “Priscilla was the first responder, at two in the morning, and she calls me on my phone, ‘Just start driving now, I’ll fill you in in the car.’ She was so calm under pressure, really quick thinking.” Chan became known in the pediatrics program “to have this black cloud,” Padrez says, “like whenever Priscilla is on, some bad stuff was going to happen. Luckily she had total capacity to deal with it.” One night when Chan was on duty alone, Padrez recalls, a mother gave birth in the parking lot across from the hospital to premature twins, just 25 weeks. “Priscilla is running the babies across the parking lot, they’re not breathing, they’re essentially dead unless she can bring them back to life.” Which she did.

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