Geoffrey

Geoffrey of Monmouth is the court geneologist and keeper of the royal library in Camelot. He first appears when he discovers the forgery of the seal of nobility Merlin created for Lancelot. (Lancelot) Though he seemed an unsympathetic character it is only through his need to do his job.

He is an old friend of Gaius. Though he refuses at first he helps Gaius by giving access to a secret volume concerning The Great Purge. It is with this that Gaius discoves Edwin Muirden's true motives. (A Remedy to Cure All Ills)

He appears once again when Merlin is searching for a weapon that Arthur could use to kill the wraith of Tristan De Bois. He tells Merlin of the old writings, which includes a tale of a weapon forged with a dragon's breath, which aids Merlin in creating the weapon and killing the wraith. (Excalibur)

Geoffrey hosted the wedding of King Uther and Lady Catrina. (Beauty and the Beast)

When he complained of a pain in his leg to Gaius (who was possessed by a Goblin). Gaius insulted him, saying he was surprised he could even stand up, and called him a "fattie". (Goblin's Gold)

Geoffrey hosted the wedding of Prince Arthur and Princess Elena where they cancelled it and told their fathers they didn't love each other. (The Changeling)

Historicity
Geoffrey of Monmouth (1100-1155) was a British writer and clergyman who composed various histories relating to Arthurian Legend. Some of his more famous works include the Historia Regum Britanniae (1136) and Vita Melini (1150).

According to one of the directors, the Geoffrey of Monmouth portrayed in this show is indeed meant to be the same Geoffrey that wrote the above books. It was percieved to be an 'interesting' idea that Geoffrey wrote these accounts as he had lived through the events described within them.