Today is the 23rd April, and although not as well recognised globally nor as celebrated as St Patrick, it is St Georges Day. Holding some significance here in the UK, well England to be be more precise, St George is the patron saint of the country lending his coat of arms as the national flag of England.
Being the patron saint of the country, it is of course inevitable that he would appear on some of the coin minted here during our long history. However, surprisingly it would not be until 1817 that it would be realised. First appearing on the gold sovereign, the design was created by famed gem cutter and engraver Benedetto Pistrucci. The same Pistrucci of the much maligned bull headed portrait of King George III (I made a post showcasing this design back in May 2017).
Given another chance, Pistrucci would create a design which has now become recognised by the coin collecting community the world over. By the late 19th century, the design would also feature on silver crowns:

With only one year (1935, shown in the centre) not featuring Pistrucci’s design. The 1935 crown was to celebrate the 25th anniversary of the accession of George V and an art deco style rendering of St George slaying the dragon was used instead.
By 1952 there was no circulating coin featuring Saint George in the UK, but in 1957 it was reintroduced with the reminting of gold sovereigns. The design would also find itself being struck on proof, brilliant uncirculated, and bullion versions of the coin.
Saint George does not only feature on British coins. He is the patron saint of many countries around the world. Ethiopia, Portugal, Brazil, Malta, Bulgaria, Serbia, Montenegro, and Georgia. He is also the patron saint of the Swiss Guard, the city of Moscow, Catalonia, Beirut, and the Kerala region in India. This list is by no means exhaustive.
Therefore examples of his image can be found on coins from Bulgaria, Russia, and Lithuania. His coat of arms have featured on Portuguese coins, and the earliest known example of his image on a coin dates from the start of the 11th century in the medieval Kingdom of Georgia (Kvirike III 1010-1037/39).