Short answers, pulled from the story.
Generalplan Ost was Nazi Germany's official plan to colonize and Germanize Central and Eastern Europe by exterminating, expelling, or enslaving the Slavic, Jewish, and other indigenous populations of the region. Full implementation was estimated to cause the deaths of more than 60 million people. The remaining populations were to be forcibly deported beyond the Ural Mountains and replaced by up to 10 million Germanic settlers.
Heinrich Himmler's SS Reich Security Main Office (RSHA) formally commissioned the plan. SS-Standartenführer Hans Ehlich and Konrad Meyer, Chief of the Planning Office of Himmler's RKFDV, were identified as the primary drafters. Himmler supervised at least five variants of the plan between 1940 and 1943.
Around 11 million Slavs were killed through systematic violence and state terrorism carried out as part of the GPO. Approximately 3.3 million Soviet prisoners of war were killed as part of the plan, and about 2 million of the 3.2 million Soviet prisoners captured by December 1941 had been killed by February 1942. Millions more were forced into slave labor.
Generalplan Ost targeted Russians, Poles, Belarusians, Ukrainians, Lithuanians, Latvians, Estonians, Czechs, Jews, and Roma. The plan assigned removal percentages to each group, ranging from nearly 50 percent of Estonians and Latvians to 80-85 percent of Poles, 85 percent of Lithuanians, and 100 percent of Latgalians.
Full implementation was not considered practicable during major military operations, and it was ultimately abandoned due to Germany's defeat. After the German defeat at the Battle of Stalingrad, resources allocated to colonization policies were diverted to the German war effort, and the extermination campaigns were practically abandoned by mid-1943.
Nearly all wartime documentation on Generalplan Ost was deliberately destroyed shortly before Germany's defeat in May 1945. Two of the three primary records were lost after the war. Historians reconstructed the plan from related memos and supplementary documents, including a memorandum by the director of the NSDAP Office of Racial Policy dated the 27th of April 1943, which came to light only in 1957.