“Though Chrétien's account is the earliest and most influential of all Grail texts, it was in the work of Robert that the Grail truly became the "Holy Grail" and assumed the form most familiar to modern readers in its Christian context. In his verse romance Joseph d'Arimathie, composed between 1191 and 1202, Robert tells the story of Joseph of Arimathea acquiring the chalice of the Last Supper to collect Christ's blood upon his removal from the cross. Joseph is thrown in prison, where Christ visits him and explains the mysteries of the blessed cup. Upon his release, Joseph gathers his in-laws and other followers and travels to the west. He founds a dynasty of Grail keepers that eventually includes Perceval.”
- WIkipedia
“In many medieval legends Joseph is credited as the first keeper of the grail. The means by which he acquired the grail are widely disputed over though the most common account is that he filled the golden chalice of the last supper with the blood flowing from Christ’s body. Robert de Boron’s book, Joseph d’Arimathe, is the first known work that credits Joseph as the grail keeper. In this version of the legend, the grail sustains Joseph through his imprisonment by the Jews. He later bequeaths the grail unto an established company of followers who found the Christian land Britain. As the legend evolved the party that travelled to Britain and first landed on the Isle of Wight has also transformed. In romances such as Perceval and Perlesvaus, it is Joseph himself who brings the grail to Britain, while in the Lancelot-Grail cycle it is Josephus, the son of Joseph, who does this. Other legends surround Joseph of Arimeathea as well. When he put his staff on the ground to go to sleep near at Glastonbury, it took leaf and flowered, becoming the “Glastonbury Thorn,” a popular pilgrimage sight before the English reformation of the 16th century. It is also speculated at the Joseph is of Christ’s own bloodline, possibly the uncle of Mary, or of Joseph. This means that, as stated in Perceval by Chretien de Troyes, the Fisher King and, indeed, Perceval as descendents of Joseph may also trace their ancestry back to Christ himself.”