President Barack Obama, who earlier this year stood at the United States of Women Summit and declared, “This is what a feminist looks like,” reiterated his stance Thursday in a powerful essay published on Glamour.com.

Describing the close proximity of his office to his living room as the “greatest unexpected gift” of his presidency, Obama wrote that he’s been able to watch his daughters, Sasha and Malia, “grow up into smart, funny, kind, wonderful young women.” He writes:

One thing that makes me optimistic for them is that this is an extraordinary time to be a woman. The progress we’ve made in the past 100 years, 50 years, and, yes, even the past eight years has made life significantly better for my daughters than it was for my grandmothers. And I say that not just as President but also as a feminist.

Publishing the essay on his 55th birthday, Obama wrote about his experiences growing up as the son of a single mother—raised, in part, by his grandmother—and watching his strong, powerful wife Michelle balance “the demands of a busy career and raising a family.”

Obama said he’s “pretty aware of the unique challenges women face—it’s what has shaped my own feminism.” But despite his unique upbringing, Obama noted, gender stereotypes still pervaded his youth, and he watches those same stereotypes impact his daughters’ lives.

“So we need to break through these limitations,” Obama wrote. “We need to keep changing the attitude that raises our girls to be demure and our boys to be assertive, that criticizes our daughters for speaking out and our sons for shedding a tear. We need to keep changing the attitude that punishes women for their sexuality and rewards men for theirs.”

The president added, “It is absolutely men’s responsibility to fight sexism too. And as spouses and partners and boyfriends, we need to work hard and be deliberate about creating truly equal relationships.”

Obama then shifted his focus to the current presidential election, writing that no matter one's political views, Hillary Clinton’s nomination “is a historic moment for America. And it’s just one more example of how far women have come on the long journey toward equality.”

“That’s what 21st-century feminism is about: the idea that when everybody is equal, we are all more free,” Obama concluded.

President Obama is the first sitting president to describe himself as a feminist. He has long championed women’s successes, including last year when he welcomed the U.S. Women’s National Soccer Team by proudly proclaiming, “Playing like a girl means you’re a badass.”

This personal essay is a powerful message to anyone who may sit on the fence of feminism: It’s up to all of us to promote equality. And in writing it, President Obama proves he’s a leader for everyone.