It was a spectacular falling out.

President Recep Tayyip Erdogan had risen to power largely thanks to the support of a preacher and fellow Islamist, Fethullah Gulen, who died this week. Mr. Gulen’s millions-strong following of educated and motivated Turks helped fill the ranks of government, as well as the media, the police and law courts, helping Mr. Erdogan run the country and cement his power.

In the early years of Mr. Erdogan’s leadership as prime minister, Gulen followers were the most prominent spokesmen for the government in Turkey and abroad. But by a decade later, Mr. Erdogan had come to resent Mr. Gulen’s reach and differences over policy emerged.

The first break came in 2013 when Gulenist prosecutors started corruption proceedings against members of Mr. Erdogan’s government and even against members of his family.

Mr. Erdogan accused Mr. Gulen of directing a “judicial coup” and moved to close down some of Mr. Gulen’s holdings in the media, as well as his lucrative education centers that prepared students for university entrance exams.

The rivalry turned deadlywhen members of a group found to be aligned with Mr. Gulen — some visited him in the United States — attempted a military coup in July 2016. Mr. Erdogan faced it down, bringing his supporters out on the streets and securing the allegiance of military and intelligence leaders who moved to arrest the coup leaders.