bedivere
In Fate/stay night Bedivere is a character associated to Saberšs memories
and he appears in some flashbacks of her past life. He probably was the
person who most cared about her, although he ignored the fact Arthuria was a
woman and not a man.
Sir Bedivere (or Bedwyr Bedrydant in his gaelic version) is one of the
traditionally associated Knights of the Round Table, together with Sir Kay.
The text in which hešs featured are various from the Mabinogion as he
appears to King Arthuršs Court to the Life of Saint Cadoc as he has to
complete the quest of rescuing princess Gwladys, daughter of King Brychan
of Brycheiniog.
Bedivere also appears in the Black Book of Carmarthen as he took part to the
battle of Tryfrwyd.
Anyway hešs most remembered, due to La Morte dšArthur by Thomas Malory,
because he was the knight who brought Excalibur back to the Lady of the Lake
after the battle of Camlann.
merlin
In Fate/stay night Merlin only appears in a few flashback concernine Saberšs past memories. He mantains his traditional function as Arthuršs (or better Arthuriašs) Court Mage and he also Consellour of the King. He looks like an old man (as the tradition implies) with a soft spot for young women (hešs kinda pervert, sadly), a misunderstood genius with odd passions. Merlin, druid, magician or prophet, is one of the most important characters of the Arthurian Cicle. Hešs the one whošs responsible for Arthuršs birth due to his magic abilities: he was also the one who looked after him in his growth (although indirectly) and who put him on the throne through Caliburnšs Proof (the Sword in the Stone). His most famous rival and apprentice is Morgan le Fay. Merlin appeared in the Breton Cycle thanks to Geoffrey of Monmouth and his Historia Regum Britanniae, although his original name was Myrddin Emrys (who canšt be confused with Myrddin Wyllt, a character who has nothing to do with Arthurian Legends). His personality isnšt that positive as we commonly believe: he was a mysterious, calculating, incoherent and somehow diabolic character, someone who doesnšt feel guilty in acting against someone else for his own interest (although hešs frankly devoted to the Kingdom he serves). Hešs the ideal advisor and scholar, the most stable support for the sovereign.
mordred
In Fate/stay night Mordred mantains his role of son (or daughter?) of Arthur/Arthuria, as the legend states. Anyway he/she is only mentioned in the game and although he/she appears in a few screenshots in the anime he/she canšt be considered as fundamental in Saberšs background. This is somethign that makes Saber story somehow different from the Arthurian Tradition. Mordred was mainly potreyed as the villain figure in the Breton cycle, especially since the Historia Regum Britanniae gaves him that role in the story of Britain. However earlier he was only considered as a knight who disagreed Arthuršs actions as King of Britain and who fought against him at Camlann. Anyway Mordred is most frequently considered as Arthuršs nephew (and in many texts also as his incestous son), who intends to usurp the throne, making an alliance with the Saxons, moving against the former king and being killed by Arthur at Camlann, assumine really negative traits and an insane personalitā traits.