Antivirus creator John McAfee, 75, has been found dead in his prison cell in Barcelona.
It came after the Spanish high court had authorised his extradition to the US, where he faces tax evasion charges.
The Catalan justice department confirmed his death following an earlier report from El Mundo newspaper.
"He was found dead in his cell apparently from suicide," said a spokeswoman for the prison system in Catalonia.
US prosecutors allege Mr McAfee failed to report income made from promoting crypto-currencies, making speaking engagements and selling the rights to his life story for a TV documentary.
The indictment, which was issued in June but only unsealed in October, said Mr McAfee failed to file tax returns from 2014 to 2018, despite receiving "considerable income" from several sources.
Mr McAfee allegedly evaded taxes by directing his income to be paid into bank accounts and crypto-currency exchange accounts in the names of others, according to the indictment.
He was also accused of evading the US tax office by concealing assets, including property, a yacht and a car, by putting them in the name of others.
If convicted, he could have faced up to 30 years in prison.
Spain's National Court earlier said it had approved his extradition to the US.
The decision could still have been appealed and the extradition would also have needed approval from the Spanish cabinet.
Since making a fortune with his eponymous antivirus software in the 1980s that still bears his name, Mr McAfee became a self-styled crypto-currency guru, claiming to make $2,000 a day.
In a tweet on 16 June, he said the US authorities believed he had "hidden crypto. I wish I did" he said.
"My remaining assets are all seized. My friends evaporated through fear of association. I have nothing. Yet, I regret nothing."