Penny Black
From Tardis Wiki, the free Doctor Who reference
The Penny Black was the brain child of Rowland Hill who for the first time suggested a one-price stamp for all- any area in the country that the person sending the letter had to pay (before then you paid to receive a letter and the cost depended on how far it had travelled).
The first printing in Bath 1840, featured the image of Queen Victoria and was part of an invasion plan of the Hobothy, who intended to use the ink as a medium for their hypnotic control. Their plan was thwarted by the Tenth Doctor and Rose Tyler. (PROSE: Stamp of Approval)
