Mustafa Koc in 2013.The billionaire chairman of Turkey’s top industrial conglomerate, Koc Holding, died Jan. 21 at a hospital in Istanbul. He was 55. (Rodger Bosch/AFP/Getty Images)

Mustafa Koc, the billionaire chairman of Turkey’s top industrial conglomerate, Koc Holding, died Jan. 21 at a hospital in Istanbul. He was 55.

The American Hospital in Istanbul said Mr. Koc died there after suffering a heart attack at his home.

Mr. Koc had been the head of Koc Holding since 2003, when he took over from his father, Rahmi Koc. The company was founded in 1926 in Ankara by Mustafa’s grandfather, Vehbi Koc, who died in 1996.

The conglomerate, now based in Istanbul, has interests in the automotive sector, durable goods, energy and other businesses. It employs about 100,000 people. Koc Holding had 2014 sales of $31.3 billion, accounting for about 5 percent of Turkey’s gross domestic product. The Koc family is among the wealthiest in Turkey.

During Mr. Koc’s term as chairman, he engineered landmark deals to expand the conglomerate, including a $4.1 billion takeover of 51 percent of Turkey’s sole crude-oil refiner from the government in 2005. In 2004, he bought 57 percent of a banking concern for $1.5 billion in a deal undertaken in partnership with Italy’s Unicredit.

“Mustafa was an outstanding business leader, a man of true integrity and a loyal friend and partner to Ford over many decades,” Bill Ford, executive chairman of Ford Motor Co., said in an emailed statement. Ford and Koc Holding have been partners for more than 80 years in motor-vehicle production in Turkey.

Koc Holding also has a joint venture with Fiat and owns many other companies, including Turkey’s biggest maker of home appliances, a heavy-vehicles manufacturer and companies producing food products and liquefied gas.

Mustafa Vehbi Koc was born Oct. 29, 1960, in Istanbul. After schooling in Switzerland, he graduated from George Washington University in 1984.

Mr. Koc had a complicated relationship with the Turkish president, Recep Tayyip Erdogan. During protests at Istanbul’s Gezi Park in 2013, demonstrators escaping police actions took refuge at a hotel owned by the Koc family. After the protests, Koc Holding was subject to extensive tax investigations by Erdogan’s government.

Forbes magazine reported that Mr. Koc’s likely successor at Koc Holding will be a younger brother, Mehmet Omer Koc, who is the company’s deputy chairman.

In addition to that brother, survivors include his wife, Caroline Giraud Koc; two daughters; his father, Mustafa Rahmi Koc; and another brother, Ali Koc.

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