Barack Obama became the first sitting US president to grace the cover of a prominent gay publication as Out magazine named him "Ally of the Year" in its latest edition.

The publication went on to describe Obama as an "ally," "hero" and "icon" for his support of LGBT rights, according to Politico.com.

"This president and his administration have ushered extraordinary change into the lives of LGBT Americans," the magazine's cover story said, as reported by NBC News.

The paper lauded Obama for his evolving attitude on homosexual marriage and for the many positive measures he has undertaken to the LGBT community, including the repeal of "don't ask, don't tell" policy.

"President Obama's evolution on marriage equality has been something to behold. He came to office reiterating that marriage was an institution reserved for a man and a woman, and continued to hold that line throughout most of his first term," the paper's cover story said.

In the Out magazine interview, Obama revealed that he started supporting gay rights after his mother taught him that everyone mattered. Obama did not support same-sex marriage until he ran for president in 2008, sources said.

"Growing up as a black guy with a funny name, I was often reminded of exactly what it felt like to be on the outside," the president said. "One of the reasons I got involved in politics was to help deliver on our promise that we're all created equal, and that no one should be excluded from the American dream just because of who they are."

The magazine asked the president who was the first gay person he ever met Obama's answer: one of his college professors) and whether he thought his daughters, Sasha and Malia, had a different attitude toward homosexuality than previous generations did.

"Absolutely. To Malia and Sasha and their friends, discrimination in any form against anyone doesn't make sense," Obama said. "It doesn't dawn on them that friends who are gay or friends' parents who are same-sex couples should be treated differently than anyone else. That's powerful."

When Obama began his first term in 2009, Out noted, only two states allowed gay marriage. Six years later, the Supreme Court legalised gay marriage nationwide in June this year with its landmark ruling in Obergefell v. Hodges.

In the interview, Obama also criticised Kentucky county clerk Kim Davis, who was jailed for refusing to issue same-sex marriage licences.

The president claimed that, just like Davis, "he is also deeply in religious freedom."

However, "at the end of the day, nobody is above the rule of law — especially someone who voluntarily takes an oath to uphold that law. That's something we've got to respect," Obama said.

The magazine cited Obama's photograph on its cover "a statement on how much his administration has done to advance a singularly volatile issue that tarnished the reputations of both President Clinton and President Bush."

"Many share credit for what has transpired, but there's no question that without the active engagement of the 44th president of the United States, who has made securing the rights of LGBT Americans a fundamental part of his legacy, we'd still be working to fulfill that dream," the magazine said. "On this issue, among many others, he is truly a great American."