Octavius or Eudaf Hen is a figure of Welsh tradition

Welsh mythology

Welsh mythology, the remnants of the mythology of the pre-Christian Britons, has come down to us in much altered form in medieval Welsh manuscripts such as the Red Book of Hergest, the White Book of Rhydderch, the Book of Aneirin and the Book of Taliesin....

. He is remembered as a King of the Britons

King of the Britons

The Britons or Brythons were the Celtic-speaking people of what is now England, Wales and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons...

 and the father of Elen Luyddog and Conan Meriadoc

Conan Meriadoc

Conan Meriadoc is a legendary British leader credited with founding Brittany. Versions of his story circulated in both Brittany and Great Britain from at least the early 12th century, and supplanted earlier legends of Brittany's foundation...

 in sources such as the Welsh prose tale The Dream of Macsen and Geoffrey of Monmouth

Geoffrey of Monmouth

Geoffrey of Monmouth was a cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur...

's Latin

Latin

Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...

 chronicle Historia Regum Britanniae

Historia Regum Britanniae

The Historia Regum Britanniae is a pseudohistorical account of British history, written c. 1136 by Geoffrey of Monmouth. It chronicles the lives of the kings of the Britons in a chronological narrative spanning a time of two thousand years, beginning with the Trojans founding the British nation...

. He also figures into Welsh genealogies.

Geoffrey of Monmouth

Geoffrey of Monmouth

Geoffrey of Monmouth

Geoffrey of Monmouth was a cleric and one of the major figures in the development of British historiography and the popularity of tales of King Arthur...

 introduces Octavius as a half-brother to Constantine I

Constantine I

Constantine the Great , also known as Constantine I or Saint Constantine, was Roman Emperor from 306 to 337. Well known for being the first Roman emperor to convert to Christianity, Constantine and co-Emperor Licinius issued the Edict of Milan in 313, which proclaimed religious tolerance of all...

, who has become King of the Britons

King of the Britons

The Britons or Brythons were the Celtic-speaking people of what is now England, Wales and southern Scotland, whose ethnic identity is today maintained by the Welsh, Cornish and Bretons...

 following the death of his father Constantius

Constantius Chlorus

Constantius I , commonly known as Constantius Chlorus, was Roman Emperor from 293 to 306. He was the father of Constantine the Great and founder of the Constantinian dynasty. As Caesar he defeated the usurper Allectus in Britain and campaigned extensively along the Rhine frontier, defeating the...

. Eventually Constantine is made Roman Emperor

Roman Emperor

The Roman emperor was the ruler of the Roman State during the imperial period . The Romans had no single term for the office although at any given time, a given title was associated with the emperor...

, requiring him to leave Britain in the hands of a proconsul

Proconsul

A proconsul was a governor of a province in the Roman Republic appointed for one year by the senate. In modern usage, the title has been used for a person from one country ruling another country or bluntly interfering in another country's internal affairs.-Ancient Rome:In the Roman Republic, a...

. Octavius, then duke of the Gewissei tribe, rebels against Roman rule, killing the proconsul and proclaiming himself king.

Constantine responds by sending three legions to Britain under the command of his great-uncle Trahern

Trahern

Trahern According to Geoffrey, Trahern was king of the Britons and Roman senator. He was the brother of the late King Coel and was sent by Emperor Constantine I to restore Britain to Roman rule during the usurpation of Octavius ....

, the brother of the late King Coel

King Cole

King Cole is a figure of British folklore.King Cole may also refer to:*"Old King Cole", nursery rhyme* Old King Cole , a 1933 Disney cartoon about Old King Cole*King Cole , Major League Baseball pitcher...

. Trahern lands at "Kaerperis" and captures it, forcing Octavius to conscript all the island into the army to combat the Roman legions. Octavius engages Trahern in a field outside Winchester and is victorious. Trahern flees to Alba

Alba

Alba is the Scottish Gaelic name for Scotland. It is cognate to Alba in Irish and Nalbin in Manx, the two other Goidelic Insular Celtic languages, as well as similar words in the Brythonic Insular Celtic languages of Cornish and Welsh also meaning Scotland.- Etymology :The term first appears in...

 (Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

) and pillages the land, and Octavious comes after him. They meet at Westmorland

Westmorland

Westmorland is an area of North West England and one of the 39 historic counties of England. It formed an administrative county from 1889 to 1974, after which the entirety of the county was absorbed into the new county of Cumbria.-Early history:...

, and Octavius was defeated and forced out of Britain. Trahern takes the crown himself, while Octavius seeks aid from King Gunbert of Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

. In Britain, supporters of Octavius ambush Trahern and kill him near London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

, allowing Octavius to return to Britain. Once arrived, he scatters the Roman forces and retakes the throne of Britain, gaining an incredible amount of wealth and prestige.

Eventually, Caradocus

Caradocus

In Geoffrey of Monmouth's Historia regum Britanniae, a fictional account of the kings of the Britons, Caradocus was titular king of the Britons in the absence of Emperor Magnus Maximus, who had left to campaign in Gaul....

, Duke of Cornwall

Duke of Cornwall

The Duchy of Cornwall was the first duchy created in the peerage of England.The present Duke of Cornwall is The Prince of Wales, the eldest son of Queen Elizabeth II, the reigning British monarch .-History:...

, suggests that Octavius marry his only daughter Helen to the new Roman Emperor, Maximianus

Magnus Maximus

Magnus Maximus , also known as Maximianus and Macsen Wledig in Welsh, was Western Roman Emperor from 383 to 388. As commander of Britain, he usurped the throne against Emperor Gratian in 383...

 (Magnus Maximus), thereby uniting the British and Roman crowns. Octavius agrees, and Caradocus' son Mauricius is sent to Rome with the proposal. However Octavius' nephew Conan Meriadoc

Conan Meriadoc

Conan Meriadoc is a legendary British leader credited with founding Brittany. Versions of his story circulated in both Brittany and Great Britain from at least the early 12th century, and supplanted earlier legends of Brittany's foundation...

(elsewhere his son) opposes the union, and nearly attacks the arriving Maximianus. Finally Caradocus restores the peace, and Octavius abdicates the throne in favor of Maximianus.