The name Brendyn is derived from the Celtic word "brenhin," which means "prince" or "leader." It originated in ancient Britain during the 5th or 6th century AD, when the Celtic tribes inhabited the region. The name was initially spelled "Brenhin" or "Brenin" in Welsh and Cornish.

One of the earliest recorded instances of the name Brendyn can be found in the Welsh Triads, a collection of traditional narratives from the Middle Ages. The Triads mention a character named "Brenhin Llyr," who was a legendary king of Britain. However, it is unclear whether this character was based on a real historical figure.

The name Brendyn gained popularity in Ireland during the Middle Ages, where it was anglicized to "Brendan" or "Brandan." One of the most famous bearers of this name was Saint Brendan the Navigator (c. 484 – c. 577), an Irish monk who is said to have undertaken a legendary voyage across the Atlantic Ocean in search of the "Promised Land of the Saints."

Another notable figure with the name Brendyn was Brendan Behan (1923 – 1964), an Irish republican, poet, and playwright. He was known for his works such as "The Quare Fellow" and "Borstal Boy," which explored the themes of Irish nationalism and social injustice.

In the 16th century, Brendyn ap Rhys (c. 1535 – c. 1609) was a Welsh poet and member of the Gorsedd of Bards, a traditional assembly of poets and musicians in Wales. He is considered one of the most important figures in the preservation of Welsh culture and language during the Renaissance period.

During the 20th century, Brendyn Behan (1923 – 1964) was an Irish novelist, playwright, and poet. He is best known for his works such as "The Hostage" and "Borstal Boy," which explored themes of Irish nationalism and social injustice.

The name Brendyn has also been popularized in modern times through various literary works and media. For instance, Brendyn Fraser is a Canadian-American actor known for his roles in films such as "The Mummy" and "School Ties."