The tank the highest number of which was made in WW II was the Soviet T-34
The T-34 is medium tank designed in the Soviet Union. It was introduced into the war in 1941. During the course of the whole war, 84,070 was manufactured. It weighs 26 tons and it was originally armed with a 76.2 mm high-velocity gun that made it superior in firepower compared to its contemporaries that year. Field Marshal von Kleist who commanded the 1st Panzer Group in Operation Barbarossa called it the "finest tank in the world" when he first encountered it. It is powered by the 38 litre Kharkiv V-2-34 diesel engine. It was a rugged vehicle with good protection and firepower suited to the Russian terrain.
The T-34
The T-34 and its successor T-34-85 (bigger gun) was made it such numbers that it was not only the mainstay of Soviet armor but also the mainstay of war movies made until this day. Several Finnish war films have been made with functioning T-34's in them. The tank with the highest number manufactured are the successor of the T-54 and T-55 series.
Below is a clip from the Russian film White Tiger (2012). It is a duel between a German King Tiger and a T-34. It allows the viewer to sense the look and sound of the tank. The Tiger in the video, by the way, is not a real Tiger. It's another tank made to look like the Tiger, IS-2, I think. It is not even powered by a petrol engine.
Here's a real Tiger, the only one in the world still working at the Bovington tank museum in England:
