In the mid 1960s, shortly after the introduction of Series C, the Bank of England proposed to introduce a new banknote series featuring people from British history. In addition to enhancing the appearance of banknotes, the complexity of the new designs was intended to make counterfeiting harder. The task of designing the new Series D notes was given to the Bank's new in-house designer, Harry Eccleston, who not only designed the notes themselves, but also created three individual portraits of the Queen. It was initially envisaged that all of the denominations of notes then in circulation would be issued under Series D. To that end, a Series D 10 shilling note was designed, featuring Sir Walter Raleigh, which would become the 50 pence note upon decimalisation, and intended to be the first of the new series to be issued. However, inflation meant that the lifespan of such a note would be too short—estimates by the Decimal Currency Board suggested that a 10 shilling note would last approximately five months; therefore, it was decided that it would be more economical to have a coin instead: the fifty pence coin was introduced in 1969. Instead, the £20 note was the first Series D note to enter circulation in 1970, with William Shakespeare on the reverse.