San Francisco 49ers quarterback Colin Kaepernick is taking a lot of heat for his refusal to stand for the national anthem at his games. But he's staying strong, thanks to the support of fellow athletes, concerned celebrities, and even the president of the United States. 

Kaepernick started his protest on August 27 during a preseason game against the Greenbay Packers. He cited concerns about police violence against people of color in the United States.

"I am not going to stand up to show pride in a flag for a country that oppresses black people and people of color," Kaepernick told NFL Media. "To me, this is bigger than football and it would be selfish on my part to look the other way. There are bodies in the street and people getting paid leave and getting away with murder."

After members of the military said they felt Kaepernick's display disrespected their service, he agreed to kneel instead of sitting out the anthem. But criticism continues to dog his protests. 

"Easy way to make sure you're NOT the starting QB on opening day,” former quarterback and ESPN analyst Matt Hasselbeck tweeted August 27.

Despite Hasselbeck’s dire prediction, Kaepernick has continued to play, and sales of his merchandise have exploded — perhaps because celebrities like J. Cole and Trey Songz have started sporting his jerseys at performances. 

Read on for quotes from Cole and Songz, and Kapernick’s other celebrity supporters.

Teammate Eric Reid joined Kaepernick’s protest before their September 1 game.

"I just wanted to show [Kaepernick] I support him," Reid told reporters. "I know there are other people in this country that feel the same way."

The two met earlier that day with former Army green beret and Seattle Seahawks long snapper Nate Boyer, who persuaded them to kneel instead of sitting through the anthem.

Seahawks quarterback Jeremy Lane also took the knee, though he does not know Kaepernick personally.

"I just like what [Kaepernick]s doing, and I'm standing behind him," Lane told reporters after the Seahawks' fourth preseason game. "It's something I plan on keep on doing, until I feel like justice is being served.”

Brandon Marshall became the fourth NFL player to join the protest on September 8.

The Denver Broncos linebacker knelt for the national anthem before the NFL's first regular-season game. Marshall and Kaepernick are long-time friends and former teammates from the University of Nevada. But Marshall told MMQB that is his protest is motivated by his own, personal experiences with discrimination.

“I’m not against the police," he said. "I’m not against the military. I’m not against America. I’m against social injustice."

Athletes from other sports joined in as well.

U.S. national team star Megan Rapinoe took the knee before a September 4 soccer game. She later told reporters that her identity as an openly-gay athlete helped her empathize with Kaepernick.

"Being a gay American, I know what it means to look at the flag and not have it protect all of your liberties," she said.

And even musicians got in on the action.

Rapper J. Cole, an outspoken supporter of the Black Lives Matter movement, sported a Kaepernick jersey at a recent show. Cole previously penned a song dedicated to "every young black man murdered in America,” after a Ferguson, Missouri police officer killed Michael Brown in 2014.

Trey Songz also repped Kaepernick's jersey at a Labor Day performance.

Songz has tweeted his support for the Black Lives Matter movement previously, saying, "Scared 4my people, Prayer so necessary."

But Kaepernick got his biggest endorsement from none other than president Barack Obama.

Though he acknowledged that the protest is difficult for members of the military to accept, Obama said on Monday that Kaepernick's "exercising his constitutional rights" by protesting.

"I'd rather have young people engaged in the argument and trying to think through how they can be part of our democratic process than those who are just sitting on the sidelines," the president said at a press conference during the G20 Summit.

This post has been updated to reflect Brandon Marshall's decision to join the protest.