t-55
Early Cold War period Soviet main battle tank.
Combined a large cannon, good crew protection, and speed in under 40 tons. Over 100k were produced (including those under licence in various Warsaw Pact countries and China) making it one of the most produced tanks of all time.
Fought in numerous wars in the Middle East, Africa, Balkans, and Asia. Currently still in service in front line units in a number of nations, as well as in reserve in more.