Undercover name for Jan Kozielewski. A non-Jewish Polish operative who brought news of the Holocaust to the West. After World War II broke out, Karski joined the Polish underground and served as a messenger for the Polish Government-in-Exile. In 1942 he was to be sent to London, where the Polish government-in-exile sat in order to issue a report on the situation in Nazi-occupied Poland - specifically regarding the status of the Jewish population. Karski wanted to provide an accurate report, and thus visited the Warsaw Ghetto on 2 occasions. Additionally he visited a transit camp for deportation to Treblinka, probably Izbica. During his visits Karski met with Jewish leaders who asked him to tell the West about the Jews' dire situation.
Karski arrived in London in November 1942. He made his report to the Polish government-in-exile, and then met with Prime Minister Winston Churchill and various other politicians, public figures, and journalists. In December, based on Karski's testimony, the Polish government asked the Allies to intervene on behalf of Polish Jewry and stop Germany from carrying out mass murder. After his stay in London, Karski traveled to the United States, where he met with President Franklin Roosevelt and others, attempting to rally the public against the Germans.
In 1982 Karski was designated as Righteous Among the Nations by Yad Vashem.