Philosopher Agnes Heller, a dissident under Hungary's communist regime and later a prominent critic of Prime Minister Viktor Orban, died Friday at the age of 90, the Hungarian National Academy of Sciences said.
Heller, who was a member of the body and a professor at the New School for Social Research in New York "died at the age of 90 on July 19," it said in a statement.
According to Hungarian news website 444.hu, Heller had not returned from a swim in Lake Balaton in the southwest of the country.
Born in Budapest in 1929, Heller studied under one of Hungary's most prominent 20th-century thinkers, the Marxist philosopher Georg Lukas (1885-1971).
She was a key member of the "Budapest School" that emerged following the bloody crushing of a 1956 uprising against Soviet rule.
Labelled a dissident and hounded by the communist regime during the 1970s, Heller -- who was Jewish, and whose father died at Auschwitz -- left Hungary and taught first in Australia and later at the New School in the United States.
She returned in the 2000s, where she became an intellectual figure of the opposition to Viktor Orban, whose government launched several smear campaigns against her.
Heller frequently spoke to world media of her worry at what she called the retreat of democratic freedoms in Hungary.
Orban's critics say that since coming to power in 2010 he has tightened his control over most key institutions, including public media, the judiciary and the education sector.
Heller was among a group of foreign intellectuals invited to France's Elysee Palace by President Emmanuel Macron following the European elections in May to mark their stand against the rise of nationalism.