Wagner was born in Vienna, Austria and joined the Nazi Party in 1931 as member number 443,217. After being arrested for proscribed National Socialist agitation, he fled to Germany, where he joined the SA and later the SS in the late 1930s. In May 1940, Wagner was part of the Action T4 euthanasia program at Hartheim with administrative functions. Due to his experience in T4, Wagner was assigned to help establish the Sobibór extermination camp in March 1942. Once the gassing installations were completed, Wagner became deputy commandant of the camp under Commandant Franz Stangl. His official title was quartermaster-sergeant of the camp. Wagner was in charge of selecting which prisoners from the newly arrived transports would be used as slave laborers in and outside the camp, and which would be sent to their deaths in the gas chambers. When Wagner was on vacation or attending to duties elsewhere, Karl Frenzel assumed his role within the camp. More than any other officer at Sobibór, Wagner was responsible for the daily interactions with prisoners. Wagner supervised the routine and daily life at Sobibór, and he was one of the most brutal SS officers. Survivors of the camp described him as a cold-blooded sadist. Wagner was known to beat and thrash camp inmates on a regular basis, and to kill Jews without reason or restraint. Inmate Moshe Bahir described him: Erich Bauer would later remark: Inmate Eda Lichtman wrote that on the Jewish fast day of Yom Kippur, Wagner appeared at roll call, selected some prisoners, gave them bread and forced them to eat it. As the prisoners ate the bread, Wagner laughed loudly, enjoying his joke because he knew that these Jews were pious. One of the Sobibór prisoners improvised a song which ironically described camp life : Wagner enjoyed this song and he forced the prisoners to sing it frequently. After two Jews escaped from Sobibór in the spring of 1943, Wagner was put in charge of a squad of soldiers from the Wehrmacht, who laid minefields around the camp so as to prevent further escapes. However, these efforts did not prevent another escape, which took form in the Sobibór revolt. Wagner was not present at the camp onthe day of the Sobibór revolt, having taken a holiday with his then wife Karin to celebrate the birth of a daughter, Marion. The inmates knew of Wagner's absence and believed that it would improve their chances of success. Wagner was considered the strictest in terms of prisoner supervision at the camp. After the successful revolt, Wagner was ordered to aid in closing the camp. He helped to dismantle and remove evidence of the camp by ruthlessly commanding the Jewish prisoners who performed this task. For instance, after the Arbeitsjuden had been transported from Treblinka and had successfully torn down the Sobibór barracks, Wagner killed them. Heinrich Himmler considered Wagner to be "one of the most deserving men of Operation Reinhard". After Sobibór, Wagner was transferred to Italy, where he participated in the deportation of Jews.
Wagner was sentenced to deathin absentia, but escaped with Franz Stangl to Brazil. Clergy at the Collegio Teutonico di Santa Maria dell'Anima in Rome assisted Wagner in his flight from justice to Syria. Wagner was admitted as a permanent resident on 12 April 1950 and on a Brazilian passport was issued in the name of "Günther Mendel", his new identity. He worked as a house-helper for a wealthy Brazilian family and then as a maker of concrete fence posts. He married a local woman who was a widow and raised her children. By 1967, his wife had died, and he was 'down on his luck' and living as a beggar in Sao Bernardo in 1971. He then found work as a farm hand and continued to live in Brazil undisturbed until he was exposed by Simon Wiesenthal and arrested on 30 May 1978. Extradition requests from Israel, Austria, and Poland were rejected by Brazil's Attorney General Henrique Fonseca de Araújo. On 22 June 1979, the Brazilian Supreme Court also rejected a West Germanextradition request. Wagner, in a 1979 BBC interview, showed no remorse for his activities in running the camp, remarking: In October 1980, Wagner was found with a knife in his chest in São Paulo. According to his attorney, Wagner committed suicide. His date of death was determined to be 3 October 1980.
