Herman Cain, the Republican pizza chain CEO who ran for president in 2012, has died after contracting Covid-19.
Mr Cain, 74, was hospitalised after being diagnosed with the disease earlier this month.
"Herman Cain - our boss, our friend, like a father to so many of us - has passed away," a message posted on his official website said.
Mr Cain, who in 2006 survived late-stage colon cancer, is one of the best-known US victims of Covid-19.
His social media accounts had been providing regular updates on his condition. On 7 July, a post from his Twitter account said "doctors are trying to make sure his oxygen levels are right".
"This is a tough virus," it said. "Please continue praying."
Mr Cain appeared without a mask at a rally held by President Donald Trump in Tulsa, Oklahoma, on 20 June.
He was admitted to hospital with coronavirus on 1 July, though it is unclear when or where he caught the infection.
The president paid tribute to Mr Cain on Thursday at the White House, saying: "He was a very special person... and unfortunately he passed away from a thing called the China virus."
Who was Herman Cain?
Born in Tennessee to a father who worked three jobs as a janitor, chauffeur and barber, and a mother who worked as a servant, Mr Cain went on to study for a degree in maths and a master's in computing.
He worked variously as a Baptist minister, a radio talk show host and as a businessman.
Mr Cain was an advocate of a flat tax system - his 9-9-9 plan - and ran for office after a stint as CEO of Godfather's Pizza.
During his run, he told reporters he would not stand for any "gotcha questions".
"And when they ask me who is the president of Ubeki-beki-beki-beki-stan-stan, I'm going to say you know, I don't know. Do you know?"
He initially proved popular, but later found himself at the centre of a number of sexual harassment allegations.
Although he denied the accusations against him, his popularity soon suffered and he suspended his campaign. Mitt Romney later became the Republican candidate in an unsuccessful race against President Barack Obama's bid for a second term in office.
In 2019, Mr Trump sounded him out to sit on the Federal Reserve Board, but he withdrew his nomination after several Republican senators refused to back his appointment.
Mitt Romney was also among those paying tribute to Mr Cain.
"Saddened that Herman Cain - a formidable champion of business, politics and policy - has lost his battle with Covid," he wrote on Twitter.
Former employee Dan Calabrese also praised Mr Cain's legacy.
"Most people heard of Herman for the first time when he ran for president in 2011. What they didn't know was his business background," he wrote on Mr Cain's official website.
"They didn't know how he had started his career as a civilian employee of the Navy. It was funny to us because sometimes political pundits portrayed him as kind of a goof - having no idea that during his time working for the Navy, he was literally a rocket scientist."
Mr Cain had enjoyed good health in recent years, Mr Calabrese wrote, but added that the previous diagnosis with cancer meant "he was still in a high-risk group" in the current pandemic.