The name Brennen has its origins in the Germanic languages, specifically the Old High German word "brinnan," which means "to burn" or "to shine." This word ultimately traces its roots back to the Proto-Germanic "brenn-an-," meaning the same. The name likely emerged during the Middle Ages in regions where Germanic languages were spoken.

One of the earliest recorded instances of the name Brennen can be found in the Codex Sangallensis, a 9th-century manuscript from the Abbey of St. Gall in modern-day Switzerland. The document mentions a monk named Brennen, who was a scribe and calligrapher. This suggests that the name was already in use by that time in the Germanic regions of Europe.

In the 11th century, a notable figure named Brennen appears in the Icelandic Sagas, a collection of historical narratives and myths. Brennen Thorvaldsson was a Viking warrior and explorer who is said to have accompanied Leif Erikson on his voyages to Vinland (present-day Newfoundland, Canada) around the year 1000 AD.

During the Middle Ages, the name Brennen was also found in various regions of Germany and the Holy Roman Empire. One notable bearer of the name was Brennen von Trier, a 13th-century Benedictine monk and theologian from the city of Trier, who wrote extensively on religious topics.

In the 16th century, a Dutch explorer and navigator named Brennen van Doesburgh sailed with the Dutch East India Company and is credited with mapping parts of the Indonesian archipelago and the coasts of Australia. His travels and contributions to cartography were significant during the Age of Exploration.

Another historically notable figure with the name Brennen was Brennen O'Rourke, an Irish chieftain and leader of the O'Rourke clan in the 15th century. He played a prominent role in the conflicts between Irish clans and the English Crown during the Tudor conquest of Ireland.

While the name Brennen has its roots in the Germanic languages, it has been adopted and used in various cultures and regions over the centuries, reflecting its historical significance and enduring appeal.