* Koc family lead Turkey’s secular business elite
* Koc businesses account for 10 pct of Turkish output
* Family had at times difficult relations with Erdogan
* Koc’s death “saddened him deeply” - Erdogan’s office (Adds comment from Bill Ford, biographical background, updates share price)
By Daren Butler and Melih Aslan
ISTANBUL, Jan 21 (Reuters) - Mustafa Koc, the 55-year-old chairman of Turkish conglomerate Koc Holding and one of the country’s most prominent businessmen, died on Thursday after a heart attack.
Head of the pre-eminent dynasty of Turkey’s secular business elite, Koc has had, at times, an uneasy relationship with the Islamist-rooted AK Party founded by President Tayyip Erdogan.
Recently there had been signs of reconciliation, however, and sources from the presidential palace said the two had met on Wednesday evening, hours before Koc died.
Koc’s businesses, which range from energy and automobiles to banking, account for close to 10 percent of Turkey’s national output and include five of its 10 largest companies.
Erdogan called Koc’s father, Rahmi Koc, and his brother, Ali Koc, to express his condolences, saying the magnate’s death had “saddened him deeply”, presidential palace sources said.
Koc collapsed while exercising and received emergency treatment from a trainer and a guard, the Beykoz state hospital, where he was first taken, said.
It said his heart was not beating when he arrived and efforts to resuscitate him began before he was transferred by helicopter to the American Hospital, a facility run by the Koc family foundation, in central Istanbul.
“Despite all the efforts of the doctors, we lost Mustafa Koc as a result of a heart attack which he suffered at home,” an official told reporters outside the American Hospital.
Shares in Koc fell as much as 5 percent after the news of his death, and were down 2.8 percent by later afternoon, while the main Istanbul share index was 1.5 percent weaker.
U.S. Ambassador John Bass, writing on his Twitter account, described Koc’s death as “a great loss for Turkey and all his friends around the world”.
From humble origins in the 1920s, the Koc empire came to represent the corporate face of Turkey’s secular Western-facing elite, part of society often viewed with suspicion by more conservative, pious segments of the population including some of Erdogan’s grass-roots supporters.
In 2013, Erdogan expressed anger with Koc’s Divan Hotel for opening its doors to protesters fleeing police during anti-government protests. The hotel called the actions humane and said accusations of backing the protests were unfair.
Commenting on the row in a March 2014 interview with Hurriyet newspaper, Mustafa Koc sought to play down any discord with political authorities but firmly defended the conglomerate.
“It is not fitting for us to fight with our state. But we have established our reputation over 90 years and we will not allow anyone to chew it up,” he said.
Subsequently, Erdogan attended an opening ceremony of a plant run by Koc’s oil refiner Tupras in December 2014, in a sign that relations were thawing.
Koc was the grandson of Vehbi Koc, who founded the group in 1926, just three years after the modern secular Turkish Republic was established out of the ashes of the Ottoman Empire.
That year, Vehbi Koc had taken over a grocery store from his father in Ankara and later become the local representative of foreign companies such as Ford Motor Co and Standard Oil.
In a statement, Ford Executive Chairman Bill Ford described Koc as an “outstanding business leader” and a close friend. “His family and mine have a special relationship that goes back to Henry Ford and Vehbi Koc. I will miss him personally and professionally,” Ford said.
Koc joined the family business after graduating from George Washington University in the United States with a business degree in 1984. In 2015, Forbes magazine ranked him as Turkey’s 26th richest man, putting his individual net worth at $1.05 billion. It said his father and two of his aunts are also billionaires.
Koc Holding companies account for 9 percent of Turkey’s exports and 18 percent of the total market capitalisation of the Istanbul stock exchange, according to an investor presentation by the group this month.
Among its companies are oil refiner Tupras, automotive manufacturer Ford Otosan, car maker Tofas and appliance maker Arcelik.
Koc had been chairman since 2003. (Additonal reporting by Can Sezer and David Dolan in ISTANBUL and Joe White in DETROIT; Editing by Ralph Boulton)