Sretko Kalinić was born on February 25, 1974, in Zadar, then part of Yugoslavia, into a Serb family. Growing up in the 1980s and early 1990s, he witnessed the turbulent and violent breakup of Yugoslavia. During the Croatian War of Independence, Kalinić joined a paramilitary unit called the Kninjas (“Red Berets”), led by Dragan Vasiljković. His time as a paramilitary fighter during the war exposed him to extreme violence and instability, experiences that would later shape his criminal career. After the war, instead of reintegrating into civilian life, Kalinić slipped into the Serbian underworld.

Relocating to Serbia, Kalinić became involved with the Zemun Clan, the country’s largest and most violent organized crime group. He quickly rose through the ranks due to his reputation for brutality, earning the nickname "Zver" (The Beast) among his peers. Testimony from former associates described Kalinić as the clan’s “favorite murderer,” entrusted with the most violent and sensitive criminal tasks. His cruelty and willingness to torture and kill without hesitation made him one of the most feared enforcers in the region.

As a leading hitman for the Zemun Clan, Sretko Kalinić played a central role in the wave of assassinations, kidnappings, and terror that swept Serbia and neighboring countries in the late 1990s and 2000s. He was a principal participant in the March 2003 assassination of Serbian Prime Minister Zoran Đinđić, a killing that shocked the nation and triggered a massive crackdown on organized crime. Kalinić, along with other Zemun Clan members, went on the run after the assassination. In 2008, he was tried and sentenced in absentia by a Serbian court to 40 years in prison for his role in multiple murders, kidnappings, and the Đinđić assassination.

While in hiding, Kalinić continued his violent activities, moving across borders with ease thanks to his dual citizenship in Croatia and Serbia. He reportedly participated in or organized the murders of at least 20 people in Serbia, Croatia, Spain, and the Netherlands, as confirmed by his own confessions and testimonies from other gang members. His methods were often shockingly cruel, including torture, dismemberment, and the use of acid to dispose of bodies. In one notorious case, Kalinić and an associate were accused of murdering a rival and disposing of his body in a Croatian lake, with only the head ever recovered.

Kalinić’s criminal career came to a violent pause in June 2010 when he was shot and wounded by fellow gangster Miloš Simović in Zagreb, Croatia. While hospitalized, he cooperated with Croatian authorities, giving testimony about the Zemun Clan’s operations and his own role in multiple murders, including the killings of witnesses linked to the Đinđić case. Initially protected from extradition due to his Croatian citizenship, legal reforms in Croatia allowed his transfer to Serbia on August 25, 2010. He is now serving a 40-year prison sentence in Serbia, his name infamous for brutality even among organized crime circles.