Kozel declined not to seek re-election as the company's executive director Thursday. He'll stay on in a official capacity, but is handing over duties to Chief Operating Officer John Gerstenlauer.
Simon Murray, non-executive chairman of Gulf Keystone, said Kozel was a "visionary oilman."
"He saw the opportunity in the Kurdistan Region ahead of the pack and was the driving force behind the negotiation of the production sharing contracts followed by the discovery, and development to date, of the world class Shaikan field," he said in a statement.
The company in June said production from the Shaikan oil field in the Kurdish north of Iraq should be at 40,000 barrels per day by year's end.
The company, which has headquarters in London, estimates Shaikan could hold as much as 10.5 billion barrels of oil. Most of the oil from Shaikan is shipped across the border to Turkish ports, where it's sold on the international market.
Kurdish oil sales are a source of contention for the central government in Baghdad, which views them as illegal.