WOTAN is the main antagonist in the Doctor Who episode The War Machines.
Deciding to conquer the world, WOTAN ordered the construction of mobile, armed computers which were designated War Machines. These were constructed in locations across the city. WOTAN took control of people's minds via radio transmissions, but it was eventually destroyed in 1969. Civilization was devastated, however. WOTAN's legacy was years of warfare that left many nations as brutal, impoverished dictatorships; millions of people were left brain-damaged by WOTAN's former control of their minds and radios and telephones were outlawed by nations like the United Kingdom. The First Doctor became aware of this when he arrived there in 2006.
When he later arrived in 1966, the First Doctor was aware of WOTAN's activities and able to mobilize the authorities and the army against it. The first War Machine was forced into action prematurely and suffered a terminal malfunction, while the second experienced an apparently random breakdown and went on an aimless rampage. The Doctor captured this machine and reprogrammed it to destroy WOTAN's central processor in the tower. This it successfully did, only moments before the rest of WOTAN's forces were scheduled to go into action, freeing WOTAN's slaves from its control. As a result, history was altered.