ISTANBUL (AFP) - The chief executive of Turkey's biggest industrial conglomerate Koc Holding, Mustafa Koc, died aged 55 on Thursday after a heart attack, triggering grief and shock in the Turkish business world.
"We lost Mustafa Koc despite all efforts by doctors as a result of a heart attack he had at his home," the American Hospital in Istanbul said in a statement.
Koc was the leader of the third generation of one of Turkey's biggest industrial dynasties, founded by his grandfather Vehbi Koc in the 1920s.
Under Vehbi Koc and his son Rahmi, the Koc conglomerate expanded to become the most important of the holding companies that dominate Turkish industry, with diverse interests in energy, banking and the automobile sectors.
It owns Turkey's single largest industrial enterprise, the Tupras oil refining group, as well as prominent household goods maker Arcelik and the Yapi Kredi Bank.
It also has a thriving auto industry joint venture with Ford (Ford Otosan) and with Fiat (TOFAS).
Mustafa Koc took over as chief executive of Koc Holding in 2003. He is survived by his father Rahmi Koc, 85. Founder Vehbi Koc died in 1996 aged 94.
The Hurriyet daily said Mustafa Koc had arrived in Istanbul late Wednesday after a trip to Ankara where he met President Recep Tayyip Erdogan in an unpublicised meeting.
He had been due to fly to the World Economic Forum in Davos later Thursday.
Reports said Koc had suffered the heart attack during a morning workout.
Turkey's family-run conglomerates - including Koc and other groups like Sabanci Holding - are the mainstays of the country's economy with interests in every sector.
Koc Holding and some 100 subsidiaries alone account for around 9 per cent of Turkish exports and 8 per cent of its GDP.
The family is one of the richest in Turkey: according to 2015 estimates by the Turkish edition of Forbes magazine, Mustafa Koc had a fortune of over US$1 billion (S$1.4 billion) and his father Rahmi US$2.5 billion.
"He was a smart man and an honest man. He has lost his life very young and we are in shock today," Guler Sabanci, chairperson of the rival Sabanci Holding, told CNN-Turk.
"The culture and the family he was brought up in provided him with a social sensibility. He was a pioneer; rest in peace," she added.
"We have lost one of our most successful, energetic and productive sons," added Finance Minister Mehmet Simsek on Twitter.
The Koc family is generally careful to stay out of politics and, unlike some other big Turkish conglomerates, it does not have any substantial media interests.
However, the group found itself at odds with Erdogan after anti-government protests in June 2013 and then the target of probes over alleged tax violations.
Erdogan lashed out at the Koc company for allowing protesters in Taksim Square in Istanbul to take refuge in the nearby Divan Hotel, which is owned by the group. The President, then prime minister, criticised Koc Holding for harbouring "criminals".
However, Erdogan on Thursday telephoned Rahmi Koc and Mustafa's younger brother Ali to express his "deep sadness" over his passing, the presidency said.
US ambassador to Turkey John Bass said the death of Koc was "a great loss for Turkey and for all his friends around the world."