Le Roux was born on 29 October 1878 into a wealthy
Bordeaux family, with no identifiable Breton origin. His father, an army medical officer, moved after his retirement in March 1882 to
Villiers-sur-Loir near
Vendôme (Loir-et-Cher), where Le Roux lived with his parents until March 1891. From 1891 to 1897 he continued his studies at the
Lycée Condorcet in Paris, where he lived until 1920, apart from a stay in London to learn English from July 1898 to June 1899. He devoted his entire life to studying
Celtic civilizations, alongside research focused on the
natural sciences and the humanities. After the death of his mother in March 1920, he moved to the north of Brittany, to the village of Saint-Hélory in
Pordic, a few kilometers from
Saint-Brieuc. Although he only learned
Breton late in his life, he was one of the main instigators of the movement for the massive creation of Breton neologisms from Celtic roots, notably on the model of
Esperanto. In permanent collaboration with the grammarian and lexicographer François Vallée, he was the author of a considerable work on the ancient Celts, ''
, published in 12 parts between 1911 and 1922, and of a History of the World
() and other essays published by the journal Gwalarn''. With François Vallée (Abherve) and Émile Ernault (Barz Ar Gouët), Meven Mordiern formed the group of "X3", passionate about Celtic antiquity, with whom he produced his great "
saga" on Celtic antiquity,
Sketla Segobrani, the apocryphal memoirs of the Celtic mercenary Segobranos, of which the first Book "Dis Atir – Teutatis" was published by Prud'homme in 1923, Books II-III in 1924 in one volume, and Book IV "
Taranis –
Esus" in 1925. The
Sketla Segobrani were illustrated by
James Bouillé, a member of the
Seiz Breur. After the war Le Roux lost his income and was reduced to extreme poverty, living on the charity of neighbours. He blamed the French government for his penury and left his papers to the United States: they are now in the Library of Congress. == Selected works ==