Billionaire Bill Gates has said he would rather pay for vaccines than travelling to Mars, which he does not think is a good use of money.
"It's actually quite expensive to go to Mars. You can buy measles vaccines and save lives for $1,000 (£814) per life saved," he told the BBC.
"And so [that] just kind of grounds you, as in - don't go to Mars."
The Microsoft co-founder also believes artificial intelligence will "pretty dramatically" transform humanity.
He said: "It will help us look into medical and scientific questions. It's not just robots, it's helping to read and write as well.
"In fact, there's been more progress there than on the robotic side. Both of them will give us much higher productivity."
Mr Gates also spoke of his surprise at becoming the face of conspiracy theories during the Covid-19 pandemic.
"I did not expect that," he said, referring to suggestions he profited from the virus, or started it himself.
"During the pandemic, there were tens of millions of messages that I intentionally caused it, or I'm tracking people. It's true I'm involved with vaccines, but I'm involved with vaccines to save lives.
"These messages sort of inverted that. I guess people are looking for the 'boogeyman' behind the curtain, the over-simplistic explanation. Malevolence is a lot easier to understand than biology."
Mr Gates also spoke about how he, like many other philanthropists, met sex offender and financier Jeffrey Epstein.
"I'm certainly more careful now than back when I did that. I'll do a little more due diligence. I may make a mistake again. I'm out in the world and I'm not trying to be a recluse."
'By my grandmother's standards, I'm crazy'
Mr Gates, who has spent much of his life as the richest person in the world, has given tens of billions of pounds to philanthropic causes, often targeted at global health, especially children.
He now divides his time between climate change, and eradicating malnutrition and diseases such as polio and malaria.
On the question of whether he is frugal in his personal life, Mr Gates said: "I don't have a gigantic closet. I don't wear jewellery. When I'm unwrapping a present, I don't take the wrapping and fold it up and use it again. My grandmother never threw a paper bag in her life or any string on a package. So by her standards, I'm crazy."
Mr Gates divorced his wife, Melinda, in May 2021. When asked if he would like to find love again, he said: "Sure, I'm not a robot."
Amol Rajan Interviews: Bill Gates is on BBC Two 19.30 GMT on Friday, and on demand on BBC iPlayer and BBC Sounds afterwards.