Well, off the top of my head, he was quite an alcoholic. Mustafa Kemal drank about a bottle of Raki a day, which is around 50% purely alcohol. He died of cirrhosis, which he had for much of his life, and no doubt from his alcohol intake.

Atatürk was also a fairly common patron of brothels in his youth, to the point where even the most positive biographies of the man I’ve read have brought this up.

I wouldn’t describe this part as being particularly “dark”, but Mustafa Kemal was very cynical about religion. He claimed to “have no religion, and at times [he’d] wish all religions at the bottom of the sea,” according to an interview with Grace Ellison in her book Turkey Today. This is a troubling matter for many conservative Turks. Many people believe he merely fought for secularism, although this aspect would suggest he had a personal distaste for religion.

Mustafa Kemal Atatürk’s presidency was, in effect, a single-party state, and open elections for the presidency only began after his death. However, Atatürk himself did attempt to introduce an opposition party to his CHP, that being the Liberal Republican Party, in order to replicate the multi-party systems of democratic nations. The Liberal Republican Party, however, would be taken in by reactionaries and conservatives who wished to eliminate Atatürk’s reforms, and its founder, a supporter of the reforms, would dissolve the party. No other party would be formed until after Kemal’s death.

Hitler apparently idolized him in some capacity. Kemal’s total ignorance of Western demands for his country, the success of the ensuing war against the Western powers, and the following recreation of Turkey in a secular and very patriotic view (and as an ethnically nearly-singular capacity) became a beacon of a Germany he could one day create. There is actually a very intriguing book on this very subject, Atatürk in the Nazi Imagination, by Stefan Ihrig, published by the Harvard Press. If you’re interested in this aspect, I recommend you check it out.

Probably the worst of Kemal Atatürk’s actions as President was his obsession with a “single Turkish people”, which no doubt was an important tenet Hitler would cling to. In the atrocities and aftermath of the Greco-Turkish War (The western front of the War of Independence), thousands upon thousands of ethnic Greeks were killed in Turkey and ethnic Turks were killed in Greece. After the war, Turkey and Greece had the population exchange, where 1.6 million people were forced out of their homes as refugees, and forced to go to Greece if they were Orthodox, or Turkey if they were Muslim. This was planned by Turkey as a means to authorize the forced migrations of Greeks from Turkey that had already began during the war, with the benefit of new Turks coming in to populate the devastated regions from both World War I and the Turkish War of Independence. This led to Turkey having a near-unilateral religion. Kemal seemed to hold an image of “Turkishness”. He believed that a religion should unify a people into one nation, and viewed the separation between Turks, Arabs, and Persians as evidence of a separate “natural religion” of each people. This actually was a famous part of one of his own works, Medeni Bilgiler.

Plenty of his foreign policy actions, such as his friendliness with both the Soviet Union and the United States, could be perceived as bad, depending on who you talk to.

Nearly all of these points are tackled in Andrew Mango’s Ataturk: The Biography of the Founder of Modern Turkey. It’s actually a very even-handed biography of the man, and I really recommend you pick it up.

Thank you for a great question!