The given name Brenna has its origins in the Celtic languages of ancient Britain and Ireland. It is derived from the Old Celtic word "brenhin," meaning "king" or "prince." This name was particularly popular among the ancient Britons and was often bestowed upon those of noble or royal lineage.

During the Middle Ages, the name Brenna was commonly found in various regions of Scotland, Wales, and Ireland. It was sometimes spelled as "Brenna," "Brynna," or "Brenna," reflecting the regional variations in pronunciation and spelling conventions of the time.

One of the earliest recorded instances of the name Brenna can be found in the ancient Welsh text known as the "Mabinogion," a collection of medieval Welsh prose stories and myths. In this text, Brenna is mentioned as the name of a character, though little is known about the individual's historical significance.

Throughout history, several notable individuals have borne the name Brenna. One of the most famous was Brenna of Galloway (c. 1020-1090), a Scottish princess and the daughter of Gille Brigte, Earl of Galloway. She is remembered for her role in the political struggles of her time and her efforts to protect her family's lands and interests.

Another notable Brenna was Brenna of Leinster (c. 1150-1225), an Irish noblewoman and the daughter of Dermot MacMurrough, King of Leinster. She played a significant role in the Norman invasion of Ireland and was known for her strategic alliances and political acumen.

In the 13th century, Brenna de Montfort (c. 1205-1252) was a French noblewoman and the wife of Simon de Montfort, a prominent leader in the Barons' War against King Henry III of England. She was renowned for her courage and resilience during the struggles of that period.

Another notable figure was Brenna of Strathclyde (c. 1280-1350), a Scottish princess and the daughter of the Lord of Strathclyde. She is recorded in historical documents as having played a crucial role in the negotiations between Scotland and England during the Wars of Scottish Independence.

In the 16th century, Brenna O'Brien (c. 1545-1610) was an Irish chieftain and the daughter of Conor O'Brien, Earl of Thomond. She was known for her leadership skills and her efforts to protect her clan's lands and traditions during a tumultuous period in Irish history.

These are just a few examples of the many notable individuals throughout history who have borne the name Brenna, a name with deep roots in the Celtic cultures of ancient Britain and Ireland.