Witold Pilecki

Born in Russia in 1901, Witold Pilecki was a member of the Polish resistance who volunteered in 1940 to be arrested and sent to Auschwitz. He was the only one to do so. For three years he gathered intelligence and organized resistance within Auschwitz, as the camp progressed from a political prisoner camp to a death camp. Over this time period, he wrote three reports on the conditions there, which were sent to England. His family was kept in the dark to protect the mission.

He took the identity of Tomasz Serafinski to protect his family and presented them to the Nazis. He allowed himself to be taken by the Nazis in Warsaw. From there he went to Auschwitz. As prisoner 4859, he organized the Union of Military Organization (ZOW) and gathered others into the resistance to make sure his goals would continue even if he was found out and killed. These men swore an oath to Pilecki and only knew about the other men in their cell (therefore protecting other cells containing other groups of resistance). Hundreds joined him in his mission. He smuggled his reports to the Polish government in London through couriers with forged German documents or on the Stockholm route.

By 1943, the Gestapo was beginning to become more stringent and Pilecki's mission was accomplished. He slipped out of camp by taking advantage of his job as a baker. Once he returned to Warsaw, he discovered that his former commanding officer had been fired and that his new boss ignored his idea of taking control of Auschwitz from within. To make matters worse, the man whose identity he stole had suffered-- he was arrested by the Gestapo for trying to escape Auschwitz and held in prison for a month. His 1944 Warsaw uprising had lasted for some time before eventually failing. Pilecki was released as a POW by American forces in 1945, and promptly joined the II Polish Corps to continue his crusade. He obtained government officials' phone numbers, documents of falsification of the People's referendum of 1946. The communists tortured Pilecki for trying to mobilize against them, and he was sentenced to death. His family was only notified of his passing years later.

https://www.jewishvirtuallibrary.org/witold-pilecki
https://www.theatlantic.com/international/archive/2012/10/the-man-who-volunteered-for-auschwitz/263083/