Whether you loved it or hated it (and in my experience, most of the people who hated it didn’t actually read it), Sheryl Sandberg’s Lean In is the seminal feminist work of our time. In her book — which has sold more than 1.6 million copies — the Facebook COO and former senior Google executive encourages women to own our ambition, go for the top job and, rather than talk ourselves out of career opportunities because they might be too hard, instead find ways to better cope with the challenges of combining ambition and family.

It’s not surprising then that what Sandberg considers to be her most critical piece of career advice actually has very little to do with work: “I truly believe the single most important career decision that a woman makes is whether she will have a life partner and who that life partner is,” she writes. “I don’t know of one woman in a leadership position whose partner is not fully — and I mean fully — supportive of her career.” She then goes on to describe her career and marriage as “inextricably intertwined.”

One of the most fascinating aspects of Sandberg’s book was its portrait of her husband Dave Goldberg — a superstar in his own right — who, in picking up his fair share of housework and childrearing, and allowing his own impressive career to take a backseat to hers, rendered him as much an icon of modern feminism as his better-known wife.

When a childbirth-related injury forced Sandberg onto crutches, it was Goldberg who rose at night with the crying baby. He taught his wife how to change a diaper when their son was eight days old. When Sandberg got the COO job at Facebook, Goldberg encouraged her to negotiate for a higher pay packet than founder Mark Zuckerberg initially offered her. Both Sandberg and Goldberg made it home by 5:30 p.m. so they could eat dinner with their kids, and both put in a few hours of work each night after the kids went to bed.

In the early years of their marriage Sandberg and Goldberg lived in different cities, she in San Francisco at Google’s headquarters, and he in Los Angeles at Yahoo. But a year after the birth of their first child, during which Sandberg struggled with the demands of a top job and single-parenting the newborn with her husband in a different city, Goldberg decided to leave L.A. — a city where the majority of his professional network was based — and join his family in San Francisco so that Sandberg could continue building her own stellar career. Goldberg’s Facebook profile is an homage to his wife — filled with posts and links to her numerous talks, interviews and articles about women, leadership and power.

While at Launch Media, a digital music company he led, Goldberg bucked the trend of not giving stretch assignments to new mothers, but continued offering up the challenges while allowing them flexible work arrangements. In university, he encouraged a female friend and prom date to “speak up” in politics class.

What Dave Goldberg understood — and embodied — is that gender equity and women’s empowerment is about men and women working together to create the conditions in which a person’s home life and work life can happily co-exist. He got that the true battleground of gender equity isn’t only in the boardroom, but also in the laundry room.

In a tragic twist, Dave Goldberg, to whom Sandberg dedicated Lean In, thanking him for “making everything possible,” died suddenly in May. It happened while he was vacationing in Mexico with his family. He went into the hotel gym for a work out and was found beside a treadmill in a pool of blood three hours later. He later died as a result of a traumatic brain injury.

With his death, the world’s foremost feminist has lost a beloved life and success partner. And the women’s movement has lost a formidable ally.