A Mysterious Black Knight Participating in the Fourth Holy Grail War
This mysterious knight clad in black armor participated in the 4th Holy Grail War serving as the Servant to Kariya Matou. He appears to have a past connection to Saber as he frequently ignores Kariya's orders to go after the female swordsman if he catches sight of her.
In reality, Berserker is Saber's fellow Knight of the Round Table known as Lancelot of the Lake. While still alive, Lancelot was the most loyal knight among Arturia's ranks. However, Lancelot winded up having an affair with Arturia's queen, Guinevere, and this fact was exposed by political enemies of the king. With Guinevere forced into execution for Arturia to save face, a distraught Lancelot killed several of his fellow knights in his attempt to save Guinevere's life. While Arturia forgave Lancelot's actions and Lancelot still pledged loyalty to her, his actions led to war and carnage throughout Britain and Lancelot was excommunicated from his duties among the Knights of the Round Table. Distraught that Arturia never admonished him for his actions, Lancelot was driven into madness and allowed himself to be summoned as a Berserker class in the Grail War so he could be slain by Arturia as atonement for his sins.
As a Berserker, Lancelot's stats are greatly augmented as a result of the Mad Enhancement ability given to the class, which comes at the cost of the knight's sanity. Unlike Hercules summoned as a Berserker in the 5th Holy Grail War though, Lancelot still retains his natural skills as a swordsman through the Eternal Arms Mastership skill which keep his skills from being dulled due to any kind of mental hindrances.
Lancelot possesses three Noble Phantasms for his use in the 4th Holy Grail War: For Someone's Glory, Knight of Honor and Arondight.
For Someone's Glory surrounds Lancelot in a dense black fog that serves to obscure his identity, status and abilities from other Servants and Masters. Its true ability is that it allows its owner to take on the form of other Heroic Spirits. But Lancelot is incapable of using For Someone's Glory to its full extent due to his mind being under the effects of Mad Enhancement. As a result, Kariya would have to make use of a Command Spell for Berserker to turn into another Servant with the Noble Phantasm.
Knight of Honor allows Lancelot to turn nearby objects he identifies as weapons into Noble Phantasms when they become consumed by the Black Knight's prana. Any objects he grabs using the ability become D-Rank weapons capable of harming a Heroic Spirit which can include anything from an uprooted electric light pole to even an F-15 fighter jet. Knight of Honor also works on the Noble Phantasms of other Servants as they still retain their ranks and abilities when they come under Lancelot's control. As a result, Knight of Honor becomes an effective counter against Gilgamesh's Gate of Babylon as Lancelot is capable of grabbing any fired weapons and making use of them to easily fend off a volley of weapon attacks coming from the King of Heroes.
Arondight is a sister sword to Saber's sword, Excalibur, which reveals Lancelot's true identity to his foe. When drawn, Knight of Honor and For Someone's Glory become sealed. However, Lancelot gains a large boost in his stats when Arondight is active and is highly effective against any magical being with a "dragon" attribute. Because Saber has dragon's blood running within her body, Arondight puts her at a great disadvantage when Lancelot draws the sword.