Legend
Richard Neville, 16th Earl of Warwick, was an English nobleman, administrator, and military commander. The eldest son of Richard Neville, 5th Earl of Salisbury, he became Earl of Warwick through marriage, and was the wealthiest and most powerful English peer of his age, with political connections that went beyond the country's borders. One of the leaders in the Wars of the Roses, originally on the Yorkist side but later switching to the Lancastrian side, he was instrumental in the deposition of two kings, which led to his epithet of "Kingmaker".
Unbeknownst to many, the Nevilles were a mage family that could trace their descent from the legendary witch Morgan le Fae. Wielding powerful sorceries they inherited from their ancestor, the gradually accrued power within their home region of northern England, becoming favorably-placed in both the Anglo-Saxon and Norman royal courts. This power reached its apex under Richard Neville, who had acquired a power base both in England (thanks to receiving the title Earl of Warwick through his marriage) and abroad (thanks to his position as Captain of the English continental possession of Calais). Incidentally, Richard and his daughter Anne (who became queen consort of King Richard III) were the closest an individual from the line of Morgan le Fae has come to possessing kingship over any part of King Arthur's original domains.
A man of many talents, Richard Neville is a Heroic Spirit who naturally qualifies for multiple classes without the need for a swimsuit or a Santa hat or a Halloween costume. In his case, the two halves of his personality can be summoned in the Saber and Caster classes, likely as a side-effect of being descended from Morgan le Fae, the legendary witch of Avalon who was said to possess three faces. The Servant Richard Neville (Darkness) who is summoned in the Saber class emphasizes his role as "one who overthrows kings".
Character
Likes: Strategy meetings, strong coffee
Dislikes: People smarter than him
Talent: Public speaking, backseat driving
Extraverted, yet passive. An eloquent, graceful figure who hides the heart of a hyena. If any one of the historical Neville's compatriots were to meet Darkness, they'd probably be more convinced of his identity compared to when meeting
his Light counterpart. Compared to Light, what Darkness inherited from the original Richard Neville is his intelligence, charisma, and truculent nature.
Richard Neville believed that the things that disqualified one for the kingship could be perceived by the mind without the heart's aid; this is the foundation of Darkness's character. Bearing Neville's intellect, he conducts himself by gathering empirical data from the surroundings and using it to chart the way forward. However, due to being left with only a sliver of the original Neville's intuitive capabilities (Richard Neville (Light)'s forte), he ends up being perceived as heartless and irresolute by others. Also, because of this lack of intuition, Darkness is susceptible to being swayed towards another's point of view, cultivating the impression of "a mercenary who only lives to destroy kings".
With regard to the Holy Grail, Darkness's wish is "to find out why Richard Neville did what he did". History did not record why the Earl of Warwick went to such lengths, and Darkness by himself can barely believe in what little records exist on this matter, as well. The best he can hope for is to retrace the original's path to try and arrive at the same unwritten beginning.
Relationships
Master
He addresses them as "my liege" and generally conducts himself as "a guest general at court". However, make no mistake: the contract is only valid for as long as Darkness's and the Master's interests align. In the end, Richard Neville (Darkness)'s true lord is himself.
King Servants
While Darkness tries to distance himself from such kinds of Servants whenever possible, some of them deliberately seek out his company to gain a leg up on their fellow monarchs.
Mordred
A distant relation who splendidly rebelled against and overthrew the inhuman King Arthur. While Darkness finds the rebellion's motivation rather pedestrian, he can't find it in himself to argue with the results.
Lu Bu
A foreign general possessing great strength and even greater lack of scruples, Darkness is naturally drawn to him. Could a collaboration with Master Chen Gong be in the cards?
Spartacus
Although they are both rebels in a certain sense, their compatibility is the absolute worst. Spartacus sees Darkness as an "oppressor behind an oppressor", while Darkness dismisses Spartacus as a fool without ambition.