Yann-Ber Kallocʼh (born Jean-Pierre Calloc'h in French; 21 July 1888 – 10 April 1917) was a Breton war poet who wrote in both Breton and French. Similarly to the English poet Wilfred Owen and the Welsh poet Hedd Wyn, Kallocʼh was killed in action during trench warfare while serving as a poilu during World War I. Kallocʼh's death was an equally catastrophic loss to Breton literature.

Yann-Ber Kallocʼh was born on the island of Groix (Breton: Enez Groe), near Lorient (Breton: An Oriant), on July 24, 1888. He was the son of a fisherman (who was lost at sea in October 1902) and his wife. He describes his childhood in the autobiographical poem Me 'zo Ganet kreiz ar e mor (I was born in the middle of the sea), which also praised his native island. Kallocʼh at first wanted to become a Roman Catholic priest and entered the minor seminary of Sainte Anne d'Auray (Breton: Santez-Anna-Wened) in 1900, then the major seminary at Vannes (Breton: Gwened) in October 1905. He was forced to renounce his vocation after his two sisters and his younger brother revealed signs of mental illness, since canon law forbade the priesthood to those who had relatives suffering from such diseases. Yann-Ber had dreamed of being a missionary and his exclusion from the priesthood brought him great distress.

He became a tutor in various cities including Paris. During his compulsory military service, Yann-Ber made a point of teaching fellow Bretons to read and write in their own language. His earliest writings were in French, but from 1905 on, he wrote in the Breton language. Taking the bardic name of Bard Bleimor (lit. "Sea Wolf", or Sea Bass), Kallocʼh wrote for cultural nationalist, pro-Catholic, and pro-devolved government newspapers. He often used to say, "I am not in the least bit French."

At the same time, Kallocʼh's contribution to Breton literature was strengthened by his literacy and fluency in both Breton and French and his ability to mix and draw equally from both literatures and cultures.

Beginning in 1912, Kallocʼh joined fellow Breton intellectuals Iwan en Diberder and Meven Mordiern in coediting the literary journal Brittia, which was intended, "to help incite in the cultivated classes of Brittany an intellectual movement of the first order, authentically indigenous and to make it take shape in the Breton language", as well as, "to contribute to reshaping Brittany into a nation, a Celtic nation."

Brittia accordingly published Diberder's literary translations of stories from Irish mythology, including the legend of the star-crossed lovers Deirdre and Naoise from the Ulster Cycle and The Voyage of Máel Dúin, into the Vannes dialect of the Breton language, but despite his role in founding the magazine, Kallocʼh felt unable to continue his involvement after Diberder began publishing attacks against the Roman Catholic clergy.

At the same time, however, Kallocʼh was one of the ten Breton intellectuals who signed the May 1913 manifesto Aveit Breiz-Vihan / Pour la Bretagne ("For Brittany"). While expressing their fear of an impending European war, the signatories expressed their intention to be loyal to the Third French Republic, while also calling for both a Breton language revival and cultural nationalism. They also called upon their fellow intellectuals from both Lower and Upper Brittany to commit nonviolent resistance to the Republic's continuing ban on Breton medium education and to both study and use Breton as a national language.

According to Ian Higgins, "When the war came, Calloc'h, like so many others, saw it as a defense of civilization and Christianity, and immediately volunteered for the front. Only Ireland and Brittany, he writes in one poem, still help Christ carry the cross: in the fight to reinvigorate Christianity, the Celtic peoples are in the van. In addition, now readily fighting for France, he saw the war as the great chance to affirm the national identity of Brittany and resurrect its language and culture."