Đorđe Kosmajac (1903 - 1942) was Serbian and Yugoslav police official and German collaborator during World War II occupation, known as deputy commandant of Banjica concentration camp.

He was born in Vlasanica, village near Vladimirci in Western Serbia. In 1926 he was employed by Belgrade City Administration, and later became official of its Special Police, which served as political (secret) police of Kingdom of Yugoslavia. He was assigned to its IV Section, dedicated to struggle against Communist Party of Yugoslavia, which had been illegal since 1921. He was efficient and advanced in ranks, but also became notorious for extracting information by beatings and torture. With his future boss Svetozar Vujković he frequented other cities of pre-WII Yugoslavia and assisted local police forces in arresting and interrogating Communists.

In late 1930s he became member of Yugoslav National Movement (ZBOR), fascist organisation led by Serbian politician Dimitrije Ljotić. Following invasion and occupation of Yugoslavia in April 1941 he, like many members of that organisation, offered his allegiance to German occupation authorities. The offer has accepted and he kept his job in Special Police, now in German service. Following anti-German uprising, he was named deputy commandant of Banjica Concentration Camp in July 1941.

His pre-war experience in fighting Communists proved helpful to Germans, because Special Police under his leadership managed to arrest many prominent Party members, thus hampering its activities in the resistance movement.

Party members, therefore, decided to assassinate him.

First attempt was made in late August 1941 when two activists - brothers Obrad and Nikola Sikimić - managed to slip strychnine in his drink. Kosmajac survived and was convinced by his physician, apparently resistance supporter, that the effects of poisoning were actually effects of weak nerves. Despite that, Kosmajac became very cautious after that.

Another assassination attempt was planned in late February 1942 by Jelena Ćetković, head of Party Local Committe. Ćetković was arrested only few days before asassination, but refused to talk under interrogation, leaving Kosmajac unaware of the planned assassination. On March 6th 1942 four activists - Đuro Majerčić, Milić Martinović, Nikola Strineka and Branko Bulat - have ambushed Kosmajac and his bodyguard Obad Zalad and had them shot. Following his death, SS General August Meyszner ordered 150 hostages to be shot at Jajinci.

In 1974 Kosmajac served as one of the basis for Nikola, character of Belgrade Special Police chief Nikola in the early episodes of Otpisani, popular WW2-themed television series. His assassination was partially reconstructed in Izdajnik, third episode of the series.