To this day, there is no clear explanation of his motives, but the facts in the case are these: on May 10, 1941, Rudolf Hess – the third most powerful man in Nazi Germany behind Hitler and Goring, flew a plane to Scotland, where he crash landed and was taken into custody. He had come on a mission of peace, trying to secure an end to hostilities between Germany and the United Kingdom.
However, his offer was quickly disavowed by the German government, and Hess stripped of al authority. He spent the rest of the war as a p.o.w., and stood trial alongside the other surviving Nazis at Nuremberg.
It seems that he had experienced some sort of guilt-motivated nervous breakdown, causing him to undertake his quixotic mission. It remains an open question whether his guilt was about the war by itself, or also about the Holocaust.