This President of the Council led the Time Lords when their power was being depleted by an unknown source, which ultimately turned out to be Omega. The President decided to use the last of their power to summon the Doctor's first two incarnations to help the current third incarnation to resolve this crisis. After this gamble proved successful, the Time Lords rescinded the Third Doctor's exile on Earth and restored his ability to travel through time and space. (DW: The Three Doctors)
The Presidents are categorised by in-universe chronological order. Loose chronological order applies for the lists, but when in doubt (as with the temporal uncertainty of the Time Wars), list them in the order in which they were first depicted as Presidents in the real world.