Robert de Boron (also spelled in the manuscripts "Roberz", "Borron", "Bouron", "Beron") was a French poet of the late 12th and early 13th centuries who is most notable as the author of the poems Joseph d'Arimathe and Merlin. Though little is known about him outside of the poems he allegedly wrote, his works and their subsequent prose redactions impacted later incarnations of the Arthurian legend and its prose cycles, particularly due to his Christian backstory for the Holy Grail.
Robert de Boron wrote his first poem for a lord named Gautier de Montbéliard and he took on the name Boron from a village near Montbéliard. What is known of his life comes from brief mentions in his poems. At one point in Joseph d'Arimathe, he applies to himself the title of meisters (medieval French for "clerk"); later he uses the title messires (medieval French for "knight"). At the end of the same poem, he mentions being in the service of Gautier of "Mont Belyal", whom Pierre Le Gentil identifies with one Gautier de Montbéliard (the Lord of Montfaucon), who in 1202 left for the Fourth Crusade, and died in the Holy Land in 1212.
Le Gentil argues that the mention of Avalon shows that he wrote Joseph d'Arimathe after 1191, when the monks at Glastonbury claimed to have discovered the coffins of King Arthur and Guinevere. His family is unknown, though the second author of the Prose Tristan claimed to be Robert's nephew, calling himself "Helie de Boron" (this is taken more as an attempt to drop a famous name than a genuine accreditation, however). Although Le Gentil describes him as a "poet endowed with boldness and piety but with mediocre talent", his work was immensely successful and influential. In particular, his version of the myth of the Holy Grail, originally an element of Chrétien de Troyes's unfinished Perceval, was adopted by almost all of the later writers of the Matter of Britain.
Robert de Boron was the author of two surviving poems in octosyllabic verse, the Grail story Joseph d'Arimathe (also known as the Metrical Joseph and the Estoire dou Graal) and Merlin; the latter work survives only in fragments and in later versions rendered in prose since, which originally happened around 1210 and possibly was done by Robert himself. The two poems are thought to have formed either a trilogy - with a verse Perceval forming the third part - or a tetralogy - with Perceval and the short Mort Artu (Death of Arthur). Collectively, it is known as the Grant Estoire dou Graal, the Roman du Graal, the Livre du Graal, and the Little Grail Cycle, or just simply as Robert de Boron's cycle (the Robert Cycle). The Didot Perceval, also known as the Romance of Perceval in Prose, a retelling of Percival's story similar in style and content to Robert's other works and attached to them, may or may be not be a prosification of the lost sections.
Robert de Boron merged the Grail myth with a Christian dimension to produce a history of the Grail. According to him, Joseph of Arimathea used the Grail (the Last Supper vessel) to catch the last drops of blood from the Christ's body as he hung on the cross. Joseph's family brought the Grail to the vaus d'Avaron, the valleys of Avaron in the west, which later writers changed to Avalon, identified with Glastonbury, where they guarded it until the rise of Arthur and the coming of Percival. Robert also introduced a "Rich Fisher" variation on the Fisher King and is also credited with introducing Merlin as born of a devil and a virgin and destined to be a redeemed Antichrist. In particular, his works have laid a foundation for, and were eventually included in a reworked form into, the Vulgate Cycle and then the subsequent Post-Vulgate Cycle, the latter of which was formerly known as the "pseudo-Robert de Boron cycle" due to the Huth Merlin manuscript's author's attribution of the entire work to Robert.
Robert de Boron appears as the fictional character Boron in Umberto Eco's novel Baudolino.