Anti-virus software entrepreneur John McAfee has been found dead in a Barcelona prison cell hours after a Spanish court agreed to extradite him to the US to face tax evasion charges.
The Catalan justice department said medics had tried to resuscitate the 75-year-old, but were not successful.
It added that "everything indicates" McAfee had taken his own life.
A controversial figure in the tech world, his company released the first commercial anti-virus software.
McAfee VirusScan helped to spark a multi-billion dollar industry in the computer world, and was eventually sold to technology giant Intel for more than $7.6bn (£4.7bn).
In October 2020, John McAfee was arrested in Spain when he was about to board a plane to Turkey, and accused of failing to file tax returns for four years, despite earning millions from consulting work, speaking engagements, crypto-currencies and selling the rights to his life story.
The US justice department alleged that McAfee evaded tax liability by having his income paid into bank accounts and cryptocurrency exchange accounts in the names of nominees.
He was also accused of concealing assets, including a yacht and real estate property, also in other people's names.
Spain's National Court authorised his extradition to the US to face the charges on Wednesday morning.
In recent years, McAfee had repeatedly claimed that there was a plot to get him - however the court said there was "no revealing evidence" that he was being prosecuted for political or ideological reasons, Spanish newspaper El Pais reported.
He had argued in a hearing earlier this month that the charges against him were politically motivated and that he would spend the rest of his life in prison if returned to the US.
But Nishay Sanan, McAfee's lawyer, said he had intended to fight all the charges.
"This is again the US government trying to erase John McAfee," Mr Sanan told NPR on Wednesday. "This man was a fighter. And in the minds of everyone who knew him, he will always be a fighter."
The entrepreneur, who was born in Gloucestershire, England first came to prominence in the 1980s when he founded his tech company and released McAfee VirusScan.
Although a pioneer of computer security, he once admitted to the BBC that he never actually used the software on his own computers - or any anti-virus software for that matter.
"I protect myself by constantly changing my IP [internet protocol] address, by not attaching my name to any device I use, and by not going on to sites where you might pick up a virus," he told the BBC's technology reporter Leo Kelion in 2013.
"Porn sites, for example, I just don't go there."
He also launched unsuccessful bids to become the Libertarian Party's candidate for the presidential elections in 2016 and 2020.
In 2019 McAfee expressed his disdain for taxes, tweeting that he had not filed tax returns for eight years because "taxation is illegal."
In the same year he was briefly detained in the Dominican Republic for allegedly bringing weapons into the country.
McAfee never fitted into the mould of what a tech entrepreneur might look like. He was brash, reckless and never far away from the next scandal.
McAfee himself is best known for the company he founded and named.
It was wildly successful and made him a rich man. He also helped to create a multi-billon-dollar computer security software industry in the process.
McAfee was a visionary, but also hot headed. It was his temperament that got him into trouble throughout his life.
In 2012 he was arrested in Guatemala, having been on the run in Belize where police were investigating the death of his neighbour.
He always denied any involvement in the murder.
A prominent libertarian, engaging speaker and crypto enthusiast, McAfee still had the ability to make money. His latest brush with law enforcement was due to alleged tax evasion on his recent earnings.
He will be remembered, rightly, as an important figure in the development of the technology scene of the 1980s and 1990s. But he will also be remembered as a deeply controversial figure, who at times seemed intent in taking a path in life that might lead to trouble.