François-Joseph-Claude Jaffrennou (15 March 1879 - 26 March 1956) was a Breton language writer and editor. He was a Breton nationalist and a neo-druid bard. He is also known as François Taldir-Jaffrennou, since he also used the Druidic name Taldir ("Wall of Steel"). He was one of the pioneers of the Breton autonomist movement.
He was born in Carnoët, the son of a notary. His mother, Anna Ropars, was from Bolazec. He went on to study law.
In August 1898, in Morlaix the Breton Regionalist Union was founded by Régis de l'Estourbeillon under the chairmanship of Anatole le Braz. Jaffrennou became secretary of the section dedicated to Breton language and literature. Between 1898 and 1899, he worked at Morlaix for the newspaper La Resistance, publishing a page about Breton literature.
On 18 July 1899, Jaffrennou visited the Eisteddfod in Cardiff with twenty one other Bretons. He was received at Gorsedd under the name Taldir ab Hernin. At this time he translated the Welsh national anthem Land of my Fathers into Breton as Bro Gozh ma Zadoù, which became the national anthem of Brittany. This hymn is now recognized and accepted by all political and cultural groups in Brittany. It was originally published in 1898 in La Résistance.
In October 1899, he moved to Rennes. There he met the editor of L’Ouest-Éclair, then in its infancy, in which he went on to publish two columns in Breton. Some time later, he founded the Federation of Breton Students. He completed his military service in Guingamp with the Dispensés platoon.
In 1901, with Jean Le Fustec, he created the Gorsedd of Brittany on the model of the Welsh Gorsedd. Having finished his law degree, he worked with his father to further his legal studies. He became acquainted with the printer Alexandre Le Goaziou and with him created Ar Vro (The Nation) whose first issue appeared on 1 March 1904. They then decided to unite to create a printshop in Carhaix. It published Ar vro and a bilingual newspaper Ar Bobl (The People), which appeared up to 1914. In 1913, he earned his doctorate from the University of Rennes for a thesis he wrote in Breton on the Breton language writer Prosper Proux.