Berserker (Fate/Zero)

"I am the shadow under the radiance of heroic spirits — Birthed of the darkness of glorious legend..."

- Berserker, Fate/Zero

Berserker is a villain from Fate/Zero who serves as the Berserker-class servant of Kariya Matou during the fourth Holy Grail War. He is voiced by Okaiyu Ryotaro.

Identity
Berserker's real identity is Lancelot of the Lake, as revealed in the final volume of the Fate/Zero novels. Until his identity was revealed, he was known simply as the Black Knight.

Lancelot, known as the Knight of the Lake, had been loyal to Arturia as a Knight of the Round Table. He was one of the few individuals that Arturia viewed as a friend, and as such was privy to the secret of her true gender, as well as the nature and properties of her sword.

Lancelot's downfall began when he fell in love with Arturia's queen, Guinevere. Though the king was actually a woman, Arturia had married in order to maintain the image of a stable royal family before the kingdom, and also to maintain the pretense that she was a male. Guinevere, in turn, willingly sacrificed her own life as a woman in order to preserve this ideal government.

When Lancelot and the queen began their affair, the Knight of the Lake considered fleeing Camelot with her, but his loyalty to Arturia and his sense of duty prevented him from doing so. When political enemies of the king exposed the affair, the queen was ordered to be executed. Left with little choice, Lancelot attempted to save her, killing several of his fellow knights including Gawain's brothers Gareth and Gaheris in the process.

Lancelot, who was considered the Perfect Knight, Guinevere, the queen who had made her beloved betray his duty, and Arturia the king who blamed herself for her loyal knight's despair, all suffered from the resulting fallout.

Although Arturia forgave Lancelot actions but Gawain still bears great hatred to Lancelot for his betrayal and the death of his brothers.

His disloyalty had fractured the balance within the Knights of the Round Table. Finally, this incident became the trigger of war and carnage, and the country shattered to pieces in the flames of war.

Lancelot even after being ex-communicated wanted to participate the Battle of Camlann to serve his King but Gawain hostilely rejected him which resulted in the debacle of his King and his country.

Personality
Lancelot is shown extreme loyalty to his King but Lancelot's guilt was, ironically, compounded by Arturia's refusal to actually blame or reprimand him for his actions. He would later admit that this made him feel it impossible to atone for his sins. In his despair, Lancelot sought escape through descent into madness to seek atonement; thus, when he became a Heroic Spirit, he was summoned as the insane Berserker.