Who introduced decimal?
It is thought that decimal numbers were used by the Elamite dynasty (Iran) approx 5000 (+/- 500) years ago.
The question 'when was a decimal currency introduced' would not be answerable, because this is lost in the mists of time. However, the use of the words 'the decimal currency' indicates that the question refers to the conversion of the British pound (aka Pound Sterling) to decimal in 1971. The Brits are not known for being in a hurry to change things.
Decimal currency was officially introduced in Britain on "Decimal Day" the 15th of February, 1971, with the Half New Penny, 1 New Penny and 2 New Pence coins being issued. The 5 and 10 New Pence coins had been introduced much earlier in April, 1968, and the 50 New Pence coins were introduced in October, 1969. The new currency consisting of 100 Pence to the Pound replaced the old currency of Pounds, Shillings and Pence…