The standard issue German anti-tank gun in 1939, it equipped the Panzerjäger battalions, Pak is short for Panzerwehrkanone - anti-tank gun, and 36 indicates the year the weapon was designed). It was arguably the best anti-tank gun in the world at the onset of war, but was quickly outclassed by heavier armour on enemy tanks. Still 15,000 were produced for Germany and its allies and it was still in service in 1945.
The Pak 36 is the anti-tank gun the Germans always defaulted to because of it's reliability and prowess. It was also relatively easy to handle and quite mobile, only needing two men to bring it into action.