Abwehr, the German military intelligence organization has been created in 1921 as a part of the Ministry of Defence. It remained small and consequently not very important part of the Wehrmacht until on January 1st, 1935 it was taken over by the soon to be Admiral Wilhelm Canaris.
In a fairly short period of time Canaris was able to reorganize his agency into one of the most efficient intelligence gathering organizations in the world. Abwehr's activities spanned through the entire world including United States, Canada, Africa and Europe including England and Russia.
With the opening of the Eastern front Abwehr was tasked with establishing Abwehr schools on the occupied territories of Poland, Baltic states and Western parts of Soviet Union. These organizations were responsible for recruitment, training and deployment of commando-style agents whose primary purpose have been the reconnaissance and sabotage behind enemy lines.
The aforementioned recruits were typically hand-picked by the Abwehr officers among millions of Soviet POWs who were captured in the first several months of the invasion. Some of them were convinced to enlist in the intelligence schools because they could no longer bear the horrible living conditions in the German POW camps, while others did this for ideological reasons, not the least of which was the hatred of Stalin's tyrannical regime in Russia.
After undergoing extensive training that included hand-to-hand combat, target practice, interrogation and intelligence gathering techniques, as well as radio operations to name a few, the graduates were supplied with absolutely the best documentation provided by Abwehr's Department 1-G responsible for false documents, photos, inks, passports and chemicals. It is important to note that German technology of producing counterfeit documents was probably the best in the world at the time. After all, they mastered the production of British pounds and US dollars that perplexed the most experienced experts on either side of the Atlantic.