Rowland Hill, an English teacher and social reformer, made it so letter sheets were issued in one penny and two penny values.
Sir Rowland Hill, KCB, FRS (3 December 1795  27 August 1879) was an English teacher, inventor and social reformer. He campaigned for a comprehensive reform of the postal system, based on the concept of Uniform Penny Post and his solution of pre-payment, facilitating the safe, speedy and cheap transfer of letters. Letter sheets were to be used because envelopes were not yet common; they were not yet mass-produced, and in an era when postage was calculated partly on the basis of the number of sheets of paper used, the same sheet of paper would be folded and serve for both the message and the address. In the same way that the first postage stamps were issued in two values (Penny Black and Two Penny Blue) both the lettersheets and envelopes were issued in one penny and two penny values in the same black and blue colours as the same value postage stamps. 
