Saber-type Servant that was first mentioned in an art book containing promotional material for Fate/Prototype. He is the Alter version of the Prototype universe's Arthur Pendragon.
Notably, Arthur Alter's Excalibur is said to be untarnished, unlike Saber Alter's Excalibur Morgan. Despite this, fandom interpretation of Arthur Alter often has him use a corrupted Excalibur similar to Saber Alter's own.
