At the time of his death, Haider was governor of the province of Carinthia and leader of the Alliance for the Future of Austria
- a party he formed after breaking away from the far right Freedom Party in 2005.
"For us, it's like the end of the world," said Haider's spokesman and the alliance's secretary-general, Stefan Petzner.
In 1999, Haider received 27 percent of the vote in national elections as leader of the Freedom Party, which ran an anti-immigrant campaign critical of European Union goals of opening membership to Eastern European countries.
Though Haider denied accusations he was pro-Nazi, the party's inclusion in the coalition government led to months of EU sanctions over his statements, which were seen as anti-Semitic or sympathetic to Adolf Hitler's labor policies.
Austria's relations with Israel also deteriorated when the party joined the federal government and Israel pulled its ambassador from Vienna.
Despite his reputation as a firebrand, Haider had significantly toned down his rhetoric in recent years. Over the summer, he staged a comeback in national politics and helped his Alliance for the Future of Austria significantly improve their standing in Sept. 28 national elections.
He and his supporters had left the Freedom Party in 2005 to form the relatively moderate Alliance for the Future of Austria. The Freedom Party's fall in popularity had been accompanied by growing infighting among party pragmatists and the rightist fringe that extended to people with links to neo-Nazi publications.
Haider had sought to distance himself from his rightist past, which included a comment in 1991 that the Third Reich had an "orderly employment policy" and a 1995 reference to concentration camps as "the punishment camps of National Socialism."
Haider, who was born Jan. 26, 1950 in Upper Austria, enjoyed tremendous popularity in the province of Carinthia. He was known by opponents and supporters alike as intelligent and politically savvy.
Chancellor Alfred Gusenbauer described the longtime politician as someone who had shaped Austria's domestic political landscape over decades.
Austrian President Heinz Fischer described Haider's death as a "human tragedy."
The impact of Haider's death on Austrian domestic politics was not immediately clear. Just last week, he and Heinz-Christian Strache, leader of the Freedom Party, met for what appeared to be a successful attempt to put aside their personal differences in light of their combined success at the polls. Taken together, the results of their two parties came to 28.2 percent of the ballot
- putting them on nearly equal footing with the winning Social Democrats.
Strache said Haider introduced a completely new political style in the 1990s and contributed to making Austrian more democratic.
"Joerg Haider achieved great things ... he was a great figure," he said.
Haider is survived by his wife, two daughters and his mother, whose 90th birthday he and his family had planned to celebrate over the weekend.