George Allen was so unpopular as a Governor that he unseated an incumbent Democratic Senator in the state he was Governor of
And then lost the two subsequent elections
And then the thread title should be changed since it is despised Governors and not politicians generally. Allen was popular as Governor and a majority liked him for many years after he was Governor. It was his actions as Senator and the shift in the state demographics that changed that.
Even when you consider the fact that his policies alienated a chunk of the electorate, that doesn't put him on the level of "Most deeply despised 'Governor" when you have Governors who went to prison, Governors who had approval ratings in the teens who are not on this list.
Edit: Just for the record I cannot stand George Allen or his confederate fanboyism and this dates back all the way to when he was supposed to be the Conservative champion in the 2008 Primaries, so about 2005.