The Gudovac massacre was the mass killing of around 190 Bjelovar Serbs by the Croatian nationalist Ustae movement on 28 April 1941, during World War II. The massacre occurred shortly after the German-led Axis invasion of Yugoslavia and the establishment of the Ustae-led Axis puppet state known as the Independent State of Croatia (NDH). It was the first act of mass murder committed by the Ustae upon coming to power, and presaged a wider Ustae-perpetrated campaign of genocide against Serbs in the NDH that lasted until the end of the war.

The Ustae used the mysterious deaths of two of their local followers as a pretext for the killings. The victims were drawn from Gudovac and its surroundings on 28 April. Most were arrested under the guise that they were rebels loyal to the ousted Yugoslav government. They were taken to a nearby field and collectively shot by a firing squad of up to 70 Ustae guards. Five of the prisoners managed to survive the initial volley and crawled away to safety. The Ustae forced Gudovac's surviving inhabitants to dig a mass grave for the victims and pour quicklime on the bodies to speed up decomposition. The following day, relatives of one of the victims informed the Germans of what had transpired. The Germans ordered a partial exhumation of the mass grave, and had 40 suspected perpetrators arrested. Mladen Lorkovi, a senior Ustae official, used his influence to have the detained men released and promised German ambassador Siegfried Kasche that the Croatian authorities would carry out a thorough investigation. No investigation took place.

An ossuary and a mausoleum were erected on the site of the massacre in 1955, as was a monument by the sculptor Vojin Baki. In 1991, amid inter-ethnic violence during the Croatian War of Independence, the monument and the mausoleum were destroyed by Croatian nationalists, as was another one of Baki's works, Bjelovarac (The Man From Bjelovar). The ruins of the ossuary were removed by the local authorities in 2002. That same year, residents signed a petition to have the Bjelovarac monument erected once again. The restored monument was unveiled in December 2010.

The Ustaše (pronounced [ûstaʃe]), also known by anglicised versions Ustasha or Ustashe, was a Croatian fascist and ultranationalist organization active, as one organization, between 1929 and 1945, formally known as the Ustaša – Croatian Revolutionary Movement (Croatian: Ustaša – Hrvatski revolucionarni pokret). Its members murdered hundreds of thousands of Serbs, Jews, and Roma as well as political dissidents in Yugoslavia during World War II.The ideology of the movement was a blend of fascism, Roman Catholicism and Croatian nationalism. The Ustaše supported the creation of a Greater Croatia that would span the Drina River and extend to the border of Belgrade. The movement emphasized the need for a racially "pure" Croatia and promoted genocide against Serbs—due to the Ustaše's beliefs grounded in anti-Serb sentiment—and Jews and Roma via Nazi racial theory, and persecution of anti-fascist or dissident Croats and Bosniaks. The Ustaše viewed the Bosniaks as "Muslim Croats", and as a result, Bosniaks were not persecuted on the basis of race.Fiercely Roman Catholic, the Ustaše espoused Roman Catholicism and Islam as the religions of the Croats and Bosniaks and condemned Orthodox Christianity, which was the main religion of the Serbs. Roman Catholicism was identified with Croatian nationalism, while Islam, which had a large following in Bosnia and Herzegovina, was praised by the Ustaše as the religion that "keeps true the blood of Croats."It was founded as a nationalist organization that sought to create an independent Croatian state. When the Ustaše came to power in the Independent State of Croatia (NDH), a quasi-protectorate puppet state established by Fascist Italy and Nazi Germany during World War II, its military wings became the Croatian Home Guard and the Ustaše Militia (Croatian: Ustaška vojnica). However, the Ustaše lacked support among ordinary Croats and never accrued any significant support among the populace. The Ustaše regime was backed by parts of the Croat population that during the interwar period had felt oppressed in the Serb-led Yugoslavia. Most of the support it had initially gained by creating a Croat national state was lost because of the brutal practices it used.The movement functioned as a terrorist organization before World War II but in April 1941, they were appointed to rule a part of Axis-occupied Yugoslavia as the NDH, which has been described as both an Italian-German quasi-protectorate, and as a puppet state of Nazi Germany.