They have both helped in the fight against COVID-19, with Mr Gates pledging $10million (£7.21million) via the Bill and Melinda Gates Foundation and Musk redirecting Tesla resources to source and produce ventilators and teaming up with the German biotech firm CureVac – of which Mr Gates is an investor.
Since last March, Mr Musk has appeared to downplay the severity of the virus, criticised stay-at-home orders and seemed to question death data.
In an interview on CNBC’s “Squawk Box” last July, Mr Gates appeared to question his involvement.
He said: “Elon’s positioning is to maintain a high level of outrageous comments.
“He’s not much involved in vaccines. He makes a great electric car. And his rockets work well. So he’s allowed to say these things.
“I hope he doesn’t confuse areas he’s not involved in too much.”
And that seemed to ruffle Mr Musk, who responded by posting multiple tweets, including “Billy G is not my lover” and “the rumour that Bill Gates and I are lovers is completely untrue”.
During a podcast interview with the New York Times, his tone seemed more serious.
He said what Mr Musk has accomplished with Tesla is ”one of the greatest contributions to climate change anyone’s ever made” and added that “underestimating Elon is not a good idea”.
Since Mr Gates met his wife at his company, their organisation has spent billions fighting causes such as infectious diseases and encouraging vaccinations in children.
The pair, along with investor Warren Buffett, are also behind the Giving Pledge, which calls on billionaires to commit to giving away the majority of their wealth to good causes.
Mr Gates stepped down from Microsoft’s board last year to focus on his philanthropic activities.