Maximilian Kolbe is an outstanding example. He was canonized by JPII
During the Second World War he provided shelter to refugees from Greater Poland, including 2,000 Jews whom he hid from Nazi persecution in his friary in Niepokalanów. He was also active as a radio amateur, with Polish call letters SP3RN, vilifying Nazi activities through his reports.
On 17 February 1941 he was arrested by the German Gestapo and imprisoned in the Pawiak prison, and on May 28 he was transferred to Auschwitz as prisoner #16670.
In July 1941 a man from Kolbe's barracks vanished, prompting SS-Hauptsturmführer Karl Fritzsch, the deputy camp commander, to pick 10 men from the same barracks to be starved to death in Block 13  (notorious for torture), in order to deter further escape attempts.  (The man who had disappeared was later found drowned in the camp latrine.) One of the selected men, Franciszek Gajowniczek, cried out, lamenting his family, and Kolbe volunteered to take his place.
During the time in the cell he led the men in songs and prayer. After three weeks of dehydration and starvation, only Kolbe and three others were still alive. He encouraged others that they would soon be with Mary in heaven. Each time the guards checked on him he was standing or kneeling in the middle of the cell and looking calmly at those who entered, while the others lay moaning and complaining, on the ground around him. He was killed with an injection of carbolic acid. Some who were present at the injection say that he raised his left arm and calmly waited for the injection.  His remains were cremated on the Assumption of Mary.