The given name Teagan has its origins in the Irish language and culture. It is derived from the Old Irish words "tadhg" or "tadhgan," which mean "poet" or "philosopher." The name gained popularity in Ireland during the early medieval period, around the 5th to 7th centuries.

The name Teagan is closely associated with St. Tegan, a 6th-century Irish missionary who traveled to Brittany, France, to spread Christianity. He is venerated as the patron saint of Guingamp, a town in Brittany, and his name is commemorated in several place names in the region.

One of the earliest recorded instances of the name Teagan can be found in the Annals of Ulster, a chronicle of medieval Irish history. The Annals mention a "Tadhgan mac Muiredhaigh" in the year 954 AD, who was the abbot of Armagh and a prominent figure in the Irish church at the time.

Throughout history, several notable individuals have borne the name Teagan. One of the most famous was Tadhg Óg Ó Súilleabháin (1667-1718), an Irish harper and composer who is regarded as one of the last great representatives of the ancient Gaelic bardic tradition.

Another notable Teagan was Tadhg Dermot O'Brien (1654-1691), an Irish Jacobite soldier who fought in the Williamite War in Ireland. He was known for his bravery and loyalty to the deposed King James II.

In the 19th century, Tadhg Gaedhlach Ó Súilleabháin (1828-1903) was a prominent Irish language scholar and lexicographer who contributed significantly to the preservation of the Irish language and its literature.

Teagan Fitzgerald (1856-1923) was an Irish politician and member of the Irish Parliamentary Party, who advocated for Home Rule and Irish independence.

Tadhg Kennelly (born 1981) is an Irish-Australian rules football player who played in the Australian Football League (AFL) for the Sydney Swans and was a part of their 2005 and 2012 premiership-winning teams.