Dragutin Dimitrijević AKA Apis
This motherfucker was the dude orchestrating the Black Hand which was behind the killing of Franz Ferdinand in Sarajevo in 1914. Although the killing marked the occassion, it was not the cause for the war, with Europe having been drifting to war far before that.
To understand just how deep this guy went, in 1903 he helped organise and participated in a coup against the reigning Obrenovic dynasty in Serbia, which had been feuding with the Karadordevic dynasty for a long time. They didn't just want to kill king Alexander, they wanted to ravage his corpse. The Italian worker at the palace who had to discard with the corpse noted that the king had many bayonet, gunshot and axe wounds, a lot after the king and queen had been killed by the initial hail of bullets. A bit over the top. With the overthrow successful, Apis was proclaimed a saviour of the fatherland and maintained a military post.
Apis, a south Slav nationalist, became the head of the Black Hand group and sponsored their activities, using them to achieve his ends of causing turmoil in Austria-Hungary. He was successful and managed to escape punishment until 1917 when the Serbian Prime Minister decided he should be offed. As a result of his scheming, the July Crisis occurred and Europe went to war. Serbia would become occupied by Austria-Hungary although it offered gallant resistance, owing more to the stupid deployment strategy of Austrian field marshal Franz Conrad von Hötzendorf.
