The Nazi Party, called the National Socialist German Workers' Party, were an extreme right wing political party originating in Germany and alongside collaborating nations attempted to conquer the world, starting with Europe in WWII. The party was initially the German Workers' Party shortly after World War I. Hitler took leadership of the party in the 1920s shortly after leaving the German Army.
They are the antagonists of the game and in the Saboteur universe, they were more scientifically advanced than the rest of the world at the time, undergoing secret experiments that could threaten the world and creating super soldiers that gained a reputation fighting on the Eastern front.