Short answers, pulled from the story.
The Chetniks were led by Draža Mihailović, a Colonel in the Royal Yugoslav Army who refused to surrender after the Axis invasion of Yugoslavia in April 1941. He established his headquarters at Ravna Gora on Suvobor Mountain and was promoted to Brigadier-General by the Yugoslav government-in-exile in December 1941.
Yes. The Chetniks collaborated with fascist Italy beginning as early as July 1941, and later with the Ustaše state and Germany directly. By 1942-1943, between 19,000 and 20,000 Chetniks in Italian-occupied parts of Yugoslavia were organised as auxiliary units of the Italian military. Direct German-Chetnik collaboration expanded after Italy capitulated in September 1943.
The Chetniks sought to create an ethnically homogeneous Greater Serbia comprising 65-70 per cent of Yugoslav territory, with the non-Serb population expelled. Their program included large-scale population transfers and the elimination of Partisans, Ustaše, Muslims, and Croats as political or ethnic competitors. They also supported the Karađorđević monarchy and opposed communism.
The Allies concluded that the Chetniks were not effectively fighting the German occupiers, while Tito's Partisans were. At the Tehran Conference of 1943, the major Allied powers decided to give exclusive support to the Partisans. Allied Special Operations Executive agents sent to Yugoslavia gathered evidence that confirmed the Chetniks were largely inactive against German forces.
Estimates of deaths caused by the Chetniks in Croatia and Bosnia and Herzegovina range from 50,000 to 68,000, with more than 5,000 victims registered in Sandžak alone. About 300 villages and small towns were destroyed, along with a large number of mosques and Catholic churches. Several historians regard these actions as constituting genocide.
The word Chetnik may derive from the Turkish çete meaning to plunder and burn down, from the Proto-Slavic četa plus the suffix -nik meaning member of a company, or from the Latin coetus meaning assembly. The first recorded use to describe army and police units appeared around the mid-18th century. By 1904, it was in common Serbian use to describe members of guerrilla bands called chete.