When Led Zeppelin put out their fourth studio album in late 1971, there was no title printed on the front. So, everyone followed the naming convention from the first three records and called it Led Zeppelin IV.
This record was a huge seller, one of the best albums worldwide (over 32 million copies, 23 million of which were sold in the US alone). It went to number 1 on the UK Album and Canadian PRM 100 charts, number 2 on the US Billboard 200, the French Album, the Japanese Album and the Australian Album charts.
