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This morning, Apple’s chief executive, Tim Cook, came out in an essay for Bloomberg Businessweek. “While I have never denied my sexuality, I haven’t publicly acknowledged it either, until now. So let me be clear: I’m proud to be gay, and I consider being gay among the greatest gifts God has given me.”

As he indicates, Cook’s revelation is no big revelation. Out magazine listed him as the second-most powerful gay person in the United States earlier this year, and Cook has never said that he is anything other than gay. But nevertheless, with his essay, Cook has become one of only a handful of openly gay chief executives in the United States — and the only one currently on the Fortune 500. What’s more, he has done it as the head of the fifth-most valuable company in the country.

Consider the glass closet shattered.

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In some ways, the corporate world has sped ahead on civil-rights and equality issues. About 90 percent of companies have workplace protections for workers on the basis of sexual orientation, and 61 percent on the basis of gender identity, according to a study from the Human Rights Campaign Foundation.

But more than half of LGBT workers hide their sexual orientation at work. A quarter worry about being passed over for promotions due to their sexual orientation, and a third worry about being stereotyped. One in five report seeking to change their place of employment and 35 percent lie about their personal lives.

That might be because the same study shows that 70 percent of non-LGBT workers “agree that ‘it is unprofessional’ to talk about sexual orientation or gender identity in the workplace.” Half admit that they would feel uncomfortable hearing an LGBT co-worker talk about his or her social life or dating. Companies can still fire a worker based on their sexual orientation in more than two dozen states, as of 2012. And very few high-ranking executives at public companies openly identify as LGBT.

But the Human Rights Campaign and other groups have shed light on the glass closet, and more executives have started to come out. That includes John Browne, the former chief executive of BP, who never acknowledged his sexuality while at the oil-and-gas giant.

“I decided very early on that the best thing was to not expose my sexuality because it would be unacceptable or dangerous,” he told NPR earlier this year. “I hope I can make up for lost time by doing what I can now to encourage people to be role models — to come out and be role models — so that people can see how you can succeed regardless of your sexuality.”

In his essay, Cook argues that he has succeeded in part because of his sexuality. “Being gay has given me a deeper understanding of what it means to be in the minority and provided a window into the challenges that people in other minority groups deal with every day,” he writes. “It’s made me more empathetic, which has led to a richer life. It’s been tough and uncomfortable at times, but it has given me the confidence to be myself, to follow my own path, and to rise above adversity and bigotry. It’s also given me the skin of a rhinoceros, which comes in handy when you’re the CEO of Apple.”

Ultimately, wanting others to benefit motivated him to acknowledge his sexuality, he said.

“I don’t consider myself an activist, but I realize how much I’ve benefited from the sacrifice of others,” he said. “If hearing that the CEO of Apple is gay can help someone struggling to come to terms with who he or she is, or bring comfort to anyone who feels alone, or inspire people to insist on their equality, then it’s worth the trade-off with my own privacy.”