Conan Meriadoc (/ˈkoʊnən/; Welsh: Cynan Meiriadog; Breton: Konan Meriadeg) is a legendary British Celtic leader credited with founding Brittany.

Both texts associate him with Magnus Maximus (Macsen Wledic, reigned 383–388), a Roman usurper against the Valentinianic dynasty who was widely regarded as having deprived Britain of its defences when he took its legions to claim the imperial throne.

The earliest undisputed evidence connecting Conan to the foundation of Brittany appears in the Life of Saint Gurthiern, included in the Kemperle Cartulary compiled between 1118 and 1127.

The prologue, the only part of the work still extant, survives in a copy by the French historian Pierre Le Baud (died 1505), but contains a passage claiming it was originally written in 1019 by a certain Guillaume, a servant of Bishop Eudo.

Rachel Bromwich suggests that Geoffrey was relying on an older tradition identifying the founder of Brittany with the prophetic Cynan, and argues that this identification is made already in Armes Prydein.

At the time Armes Prydein was composed, the Breton nobility under Alan II, Duke of Brittany had forged an alliance with Æthelstan, king of England, in the face of Viking attacks on their territory.

[4] The story of Conan is attested in several medieval sources, the most substantial versions being those included in Geoffrey of Monmouth's Historia Regum Britanniae and the Welsh tale known as The Dream of Macsen Wledig.

He does so, and repels numerous attacks from the Gauls and Aquitanians, and asks for British wives for his men from Maximianus' regent Dionotus, with whose daughter, Saint Ursula, he was said to be "most passionately in love", as reflected in her legends.

Maxen Wledig (Magnus Maximus), here portrayed as the rightful Roman Emperor rather than a usurper, sees Elen and her kingdom in a dream vision, and seeks her out and marries her.

[8] Meriadoc appears in one of the genealogies from Jesus College MS 20, which traces the descent of Geraint mab Erbin, king of Dumnonia in the West Country, back to "Cynan map Eudaf Hen".