Indeed, until the late 20 century, the day was more widely embraced by the honorary Irish in places such as Australia than it was in Ireland. 

Amid the festivities is a parade of stereotypes - leprechauns, shamrocks, the colour green and, of course, a pint or 10 of Guinness at the local Irish pub.

But ask a Guinness-soaked green-clad publican who St Patrick was and, at best, you might draw an incoherent answer about the Emerald Isle's snake-free pastures.

Spoiler: There were never any snakes in Ireland. According to science, this has more to do with geography than St Patrick's powers of repulsion.

But as the enduring legend reveals, St Patrick - the patron saint of Ireland - is steeped in mythology.

Beneath the embellishment, it is generally agreed that St Patrick was a 5th-century Romano-British Christian missionary, who was born in Britain in AD 387. His name, before adopting "Patrick", was thought to be Maewyn Succat.

When he was 16, he was kidnapped by Irish raiders and taken as a slave to Ireland. Legend has it he was sold to a druid chief and for six years he worked as a herdsman. While among the sheep, he supposedly "found God". He escaped and returned to his family in England where he eventually became a priest. 

He took the Christian-Roman name of Patricius, which was later known as Patrick.

In his 30s he returned to Ireland, to convert the pagan Irish to Christianity, supposedly using the three leaves of a shamrock to explain the Christian holy trinity: the Father, the Son, and the Holy Spirit. 

Over three decades, he is said to have travelled the Emerald Isle, establishing monasteries, schools and baptising and ordaining priests. 

His encounters with the pagan druids, many of whom resisted the rapid cannibalisation of their old religion by Christianity, are said to have inspired the allegory of St Patrick driving the snakes from Ireland. 

While legend credits St Patrick's evangelising with converting the Irish to Christianity, historians believe there were already Christian believers in Ireland by the time Patrick arrived. The religion is likely to have been spread through Ireland's strong trading links with the Roman empire.

It is believed St Patrick died on March 17 in 461AD and was buried at Downpatrick.

It is a national holiday in Ireland, and on the island of Montserrat in the Caribbean, which was founded by Irish refugees. It is a bank holiday in Northern Ireland and a provincial holiday in the Canadian province of Newfoundland.

As the day falls during Lent, Christians have historically been given a reprieve on their Lenten food and alcohol restrictions, contributing to the day's strong association with traditional Irish beverages - Irish whisky, beer and cider. 

Popular Irish toasts on St Patrick's Day, include: "may the roof above us never fall in, and may we friends beneath it never fall out."