The name Brandan originates from the Irish language and culture, first appearing in the early medieval period around the 5th to 7th centuries AD. It is derived from the Old Irish word "brenn," meaning "prince" or "noble." The name was likely a compound of this word and a suffix like "-an" or "-án," which was used to form personal names.

One of the earliest and most famous bearers of this name was Saint Brendan the Navigator, an Irish monk born around 484 AD. He is renowned for his legendary voyage across the Atlantic Ocean, as recounted in the medieval text "Navigatio Sancti Brendani Abbatis" (The Voyage of Saint Brendan the Abbot). This text, which dates back to the 9th century, describes Brendan's journey to the "Promised Land of the Saints," which some scholars believe may have been a reference to North America.

Another notable figure named Brendan was Brendan of Clonfert, an Irish monastic saint who lived in the 6th century AD. He founded the famous Clonfert Monastery in County Galway, Ireland, and is venerated as one of the Twelve Apostles of Ireland for his missionary work.

In the 9th century, Brendan of Birr, also known as Brendan the Elder or Brendan the Navigator, was an Irish abbot and monastic founder. He is credited with establishing the monastery of Birr in County Offaly, Ireland, and is associated with several legends and miracles.

Fast-forwarding to the 16th century, Brendan O'Rourke (c. 1490–1562) was an Irish chieftain and Lord of West Breifne, a territory spanning parts of modern-day counties Cavan and Leitrim in Ireland. He played a significant role in the political and military conflicts of his time, particularly in his resistance against the English Tudor conquest of Ireland.

In the 20th century, Brendan Behan (1923–1964) was a renowned Irish poet, short story writer, novelist, and playwright. He is best known for his autobiographical works, including "Borstal Boy" and "The Quare Fellow," which shed light on the harsh realities of prison life and the Irish Republican movement.