Originally called Archetype Saber, he is the version of Saber that was to be used in the original Fate/stay night novel that was penned and left uncompleted. He would later make an official debut in Fate/Prototype as a Saber from an entirely different time tree, complete with his own characterization and contextual differences compared to the Saber from Fate/stay night.
Arthur's parameters differ from Artoria's as well; he sacrifices Mana and Luck for greater Strength and Endurance. This is similarly reflected in their fighting styles; whereas Artoria fights very elegantly and supplements her swordplay with her Servant Skills, Arthur fights very functionally, almost coldly, and funnels his skills into his martial prowess.
Arthur plays a prominent background role in Fate/Grand Order as well: he is chasing Beast VI across time and space, with the intent to slay it for good after unsuccessfully attempting such in 1991 and 1999 of his own time tree.
