Brother Bernard was a priest who lived in Ireland in 1006. He served as the chief librarian at the Abbey of Kells, where the Book of Kells was stored. The book was crucial to the ongoing power struggle between the Norse King Sitric Silkbeard of Dublin and the Irish-born King Brian Boru of Munster in the early 11th century. Although it was written on the Scottish island on Iona in the 8th century, it is a powerful symbol of Irishness. Sitric was concerned that if Brian gained possession of the book, he would be able to use it to gain control of Dublin and Ireland as a whole. In 1006, he sent one of his warriors, Olaf Eriksson to enlist Brother Bernard's assistance in protecting the book so as to prevent Brian from using it as a pawn to place himself on the throne of Dublin.
However, the Eighth Doctor and his companion Tamsin Drew almost entirely derailed Sitric's plot as they were labouring under the misapprehension that Brother Bernard was the Doctor's old enemy and fellow renegade Time Lord, the Monk. In actuality, Abbot Thelonious was the Monk, who sought the Book of Kells as he had instructed the monks at the Abbey to re-create a vital part of the directional unit of his TARDIS, which the First Doctor had stolen many years earlier in their respective personal timelines.
Although Sitric's plan to keep the book out of Brian's hands was successful, his position was further destabilised by a second revolt in Leinster several years later and the Battle of Clontarf in 1014. The Doctor warned Brother Bernard to stay away from Clontarf during that year. (AUDIO: The Book of Kells)