Anders Behring Breivik, born 13 February is a Norwegian accused mass murderer and the confessed perpetrator of the attacks in Norway. On 22 July Breivik bombed the government buildings in Oslo, which resulted in eight deaths. He then carried out a mass shooting at a camp of the Workers' Youth League of the Labour Party on the island of Utøya where he killed 69 people, mostly teenagers.

Breivik was diagnosed with paranoid schizophrenia by the court-appointed psychiatrists. According to their report, Breivik acted compulsively based on a delusional thought universe. Among other things, he alluded to himself as a future regent of Norway pending a takeover by a Templar-like organization. Imagining himself as regent, his ideas included organizing Norwegians in reservations and using them in breeding projects. Other psychiatrists disagree that he is psychotic or schizophrenic, and on 13 January after much public pressure, the Oslo district court ordered a second expert panel to evaluate Breivik's mental state. On 10 April the second psychiatric evaluation was published with the conclusion that Breivik was not psychotic during the attacks and he was not psychotic during their evaluation, rather he is an extreme narcissist and sociopath.

Breivik's far-right militant ideology is described in a compendium of texts, titled – A European Declaration of Independence and distributed electronically by Breivik on the day of the attacks. In it he lays out his worldview, which includes support for cultural conservatism, ultranationalism, right-wing populism, Islamophobia, Zionism, anti-feminism, and White nationalism. It also expresses support for paramilitaries such as the Scorpions. It regards Islam and cultural Marxism as the enemy, and argues for the violent annihilation of "Eurabia" and multiculturalism, and the deportation of all Muslims from Europe (culminating in the year)to preserve European Christendom. Breivik wrote that his main motive for committing the atrocities on 22 July was to market this manifesto.