Kokoreç is most probably an invention of the nomadic sheep herders of the Central Asian Plateu, and brought by these travelers to Anatolia where it became a tradition over the past 100 years. Being of people not to waste any part of the animal, the nomads devised a way to spool the sheep intestines around a pike and roast them over the fire. Intestines are naturally chewy so the Kokoreç is chopped into small pieces and mixed with thyme, oregano, salt, pepper, and often times fresh tomato and parsley. The mixture is then added to a bread roll to form a sandwich.
In modern times, while the EU has banned the sale of Kokoreç, in Turkey it is still widely available and as far as I know completely safe to consume. It is a traditional midnight snack of those who have imbibed among the bustling crowds of bar and pub streets throughout the city.
Here is a short clip showing how Kokoreç is prepared.
Here is a map showing how to find Kral Kokoreç, one of the best in Sirkeci:
View Kral Kokorec in a larger map