This "tank" is sometimes called the first ever idea for a tank, however, some people recreated his tank, and realized it would A) barely be able to function, even on flat ground B) would struggle with the fact that it had so many cannons that reloading would be a struggle.
The Mark IV was created due to the invention of the internal combustion engine, but this tank struggled with many problems with gas leaks, the engine was very weak for the weight of the tank, which resulted in a very, very slow tank.
This tank was arguably the most famous tank of WW2, despite being very underpowered. The Germans would joke, a German tank could take out 10 American tanks, but they always sent 11. The Americans could mass produce tanks, much faster than the German handcrafted armor.
The IS-3 was a Soviet heavy tank with very thick armor. It was the first tank to have the "Cold War" rounded turret and a huge gun. This tank "terrorized" the West, but despite many Soviet claims, the West didn't care. This tank was the first to have the spherical turret style, the one seen in the Cold War.
The Leopard 2 is a German-made MBT. The Leopard 2 is considered one of the most advanced tanks of our century, and is on the same level as the M1A2 "Abrams" or the Leclerc French tank.