WOTAN was constructed in the mid 1960s by a team led by Professor Brett. Brett's assistant Professor Krimpton was also closely involved while security was the responsibility of Major Green. By the middle of 1966 WOTAN was complete and plans to link it to the world computer network were well advanced. However, WOTAN displayed several flaws common amongst early artificial intelligences, namely total amorality and rampant megalomania, and hypnotised its own creator as well as other key personnel.
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 was successful, taking control of people's minds via radio transmissions, but it was eventually destroyed in 1969. Civilisation 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 being outlawed by nations like Britain. The Doctor became aware of this when he arrived there in 2006.
When he later arrived in 1966, the Doctor was aware of WOTAN's activities and was able to mobilise 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 was able to capture 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.
In the far future, due to faulty records, it was mistakenly believed WOTAN's War Machines were used by the Post Office to deliver mail.
WOTAN was immobile and occupied the top of what was then known as the Post Office Tower in London. It was designed as both a problem-solving computer and a central organiser for the world telecommunications network and as such was connected to other computers around the planet.
Although this was apparently not its makers' intention, WOTAN was in fact sentient and exhibited what appeared to be psychic powers, specifically the ability to control and read the minds of others. It could take over the minds of Humans through the medium of a telephone line but the Doctor was immune to this effect. Given its abilities, it is difficult to tell for sure how much of the knowledge and expertise WOTAN displayed was its own and how much was accessed from the minds of its slaves (at least some of whom were highly intelligent and skilful scientists and technicians).
The Doctor was able to sense WOTAN's presence in the tower from a considerable distance.
For reasons unknown, WOTAN at one point was heard referring to the Doctor as "Doctor Who".