Mr. Lundstrom was a supporter of far-right causes and, at one point, an unsuccessful candidate for office. He was convicted of aiding copyright infringement in 2009.
Carl Lundstrom, the heir to a Swedish crisp bread fortune who financed the Pirate Bay, a notorious file-sharing service that was popular in the mid-2000s, was killed on Monday in a small plane crash in Slovenia, according to Alternative for Sweden, the far-right party that he supported.
Mr. Lundstrom, 64, was the pilot and sole occupant of the plane, a Mooney M20, which had taken off from Zagreb, the Croatian capital, and was en route to Zurich, the party said in a statement.
Air traffic controllers reported that they had lost contact with the plane in the mountainous Velika Planina area of northern Slovenia, according to the Slovenian police.
Extremely bad weather made it impossible for rescuers to use helicopters, forcing them to take a gondola and then hike on foot to reach the remote crash site, the police said. They discovered pieces of the plane lodged in a wooden hut, which was practically cut in half, the police said.
A body was later found amid the rubble, said the police, who added that the cause of the crash had not been determined.
Mr. Lundstrom was a grandson of the founder of the Swedish crisp bread brand Wasabröd, and an heir to the company fortune, according to Swedish media reports.