The Winter King: A Novel of Arthur is the first novel of the Warlord Chronicles trilogy by Bernard Cornwell, originally published in the UK in 1995 by Penguin Group.

However, on the cusp of a united peaceful Britain, Arthur's decision to marry Guinevere plunges the island into war again.

The story is narrated by its main protagonist, Derfel Cadarn, an elderly monk who has converted to Christianity late in life after spending many years as a warrior in the service of Arthur, a renowned warlord who long ago fought to protect the kingdom of Dumnonia.

In the monastery at Dinnewrac, the young Queen Igraine begs Derfel to record his tales of how he met the many famous heroes of Arthurian legend.

Uther, a pagan, finally loses patience with Norwenna's Christian midwives and summons Merlin's priestess Morgan to deliver the child.

While Derfel is with him, Owain enters into an agreement with Prince Cadwy of Isca to massacre a group of Cornish tin miners who had been working in Dumnonia at Uther's invitation.

When Prince Tristan, Edling of Kernow, arrives in Dumnonia and demands recompense for the massacre, Owain blames an Irish raiding party.

To do this, he enters into a peace treaty with Powys: he will return Gundleus to the throne of Siluria and then marry Ceinwyn, the daughter of Gorfyddyd.

He abandons Ceinwyn and marries Guinevere, destroying any hope of alliance and plunging Britain back into civil war.

In the years following Arthur's marriage to Guinevere, Derfel grows into a great warrior and is given a second name, "Cadarn", meaning "The Mighty".

Galahad explains in private that Lancelot will not take defeat lightly and suggests that Derfel leave Ynys Trebes immediately.

Derfel then spends three years in Benoic and learns quickly that Lancelot's fearsome reputation has nothing to do with his prowess in battle and everything to do with paying poets to sing his praises.

As a great massacre ensues, Derfel feels compelled to return to the palace, where he finds King Ban resigned to his fate and Father Celwin in the library frantically searching for a particular Roman scroll, both refusing to leave.

Derfel arrives in time to hear this slander, declaring Lancelot a liar and challenging him to back up his story with his sword, but Arthur defuses the situation.

Derfel is rewarded for his service to Arthur and is declared a lord, but shortly after learns that Merlin has gone north instead of to the Isle of the Dead.

Meeting with Aelle, Arthur negotiates three months of peace in exchange for the gold and information on how to capture the Powysian stronghold of Ratae.

In private Merlin tells them that Gorfyddyd is lying and that he will kill Mordred in order to fulfill his ambition of becoming High King.

Upon Galahad and Derfel's return to Glevum Tewdric refuses to commit his troops to the war, believing that Gorfyddyd was telling the truth and that Mordred will be safe.

Eventually Arthur gives up on Tewdric and his sworn men, including Derfel and Galahad, march north to confront Gorfyddyd alone.

Derfel and his men undertake a night march to reach and capture Lugg Vale at dawn, guided by Nimue, who has an uncanny ability to find her way in the dark.

Arthur arrives in time to destroy the vanguard of Gorfyddyd's army and sends Galahad south in the hope that the men of Gwent will come and fight now that they know battle has begun.

A handful of men from Kernow do arrive led by Prince Tristan, who wishes to repay Arthur for fighting against Owain.

Before the battle can recommence Merlin arrives and commands both armies to cease hostilities because he needs all Britons to help him in his quest for the Cauldron of Clyddno Eiddyn, one of the lost Thirteen Treasures of Britain.

Merlin, turning to Derfel, informs him that he has persuaded Oengus Mac Airem's Blackshield Irishmen, previously allied to Gorfyddyd, to switch sides and give Arthur victory.

The series was developed for television by Kate Brooke and Ed Whitmore, premiering on ITVX in the United Kingdom on 21 December 2023.

Publishers Weekly called it an "exemplary kickoff to a trilogy about the legendary warrior-king", adding that "Cornwell's Arthur is fierce, dedicated and complex, a man with many problems, most of his own making" and that "Cornwell knows his history--the battle scenes are particularly fine--but not once does it get in the way of people of flesh and blood meeting on a darkened field of combat.

"[4] According to Kirkus Reviews, the book's "great battle scenes and brilliant political intrigue swirl about a cast of legendary but very human characters.

"[5] The Washington Post remarked that the "strength of the tale lies in the way Cornwell tells it through the creation of flesh-and-blood players who make a historical period come magically alive.

"[7] An Amazon.com editorial review said it is essentially "a modern political thriller, told in flat American diction... Bernard Cornwell downplays the magic that enlivens the traditional stories, depicting it more as a combination of superstition and shrewd wits" and recommended it "with reservations; though it's absorbing to read, the emphasis on battles and politics means that this will greatly appeal to some fantasy readers, but disappoint others.