Just 7 Years Ago, The CEO Of BP Quit His Job Because He Didn't Want People To Know He Was Gay

After all, Cook's sexuality was not a secret within the tech and business communities, and many companies these days, including Apple, have explicitly supported same-sex marriage and other issues close to the gay community.

What is especially notable about Cook's announcement is how drastically the climate has changed for gay people in corporate America, even in the past 10 years.

The case of Lord John Browne, who began his tenure as CEO of BP in 1995, underscores just how fast attitudes have shifted.

For years, the executive hid his sexuality from his peers in favor of carrying with him a constant fear that someone, somewhere might have discovered he was gay.

And in 2007, he resigned from his CEO job three months earlier than planned in hopes of preventing a London tabloid from continuing to report on his relationship with Jeff Chevalier, a man he met through the escort agency Suited and Booted.

The early resignation cost Browne more than $30 million in stock and retirement benefits, and he blames the decision on his years of leading a double life.

"If you want to hide your sexuality, it's very difficult to find people in the open," he explains to NPR's Audie Cornish in an interview that aired this past June. "Therefore, you might go elsewhere and you begin to create a pretty dangerous situation."

Earlier this year, he published the book, "The Glass Closet: Why Coming Out Is Good Business," which includes interviews with other gay executives about their experiences in the workplace and the discrimination they received.

In it, he expresses regret at not coming out during his time at BP and encourages other prominent business leaders to do so. In fact, he told Businessweek in June that workers who disclose their sexuality make their companies more profitable by allowing themselves to focus on doing their work instead of maintaining a heterosexual image.

In a statement provided to Business Insider, Browne called Cook's decision to make his sexuality public, "an important step in the journey towards full and uncompromising inclusion of LGBT people."

"By deciding to speak publicly about his sexuality, Tim Cook has become a role model, and will speed up changes in the corporate world," Browne says. "It is a significant moment for Tim, for Apple, and for LGBT people everywhere who continue to grapple with their own private struggles."