Sir Ironside is the Red Knight of the Red Launds, the warrior who has laid siege to Dame Lionesse at Castle Dangerous. He is Gareth’s final and most dangerous opponent in the Tale of Sir Gareth.

Ironside must be distinguished from Sir Perimones. Perimones is one of the four brothers encountered earlier in the journey and is called the Red Knight by Malory, although later summaries often distinguish him as the Puce Knight. Ironside is a separate character, is not related to those four brothers and bears the fuller title Red Knight of the Red Launds or Red Lawns.

Ironside has maintained the siege of Castle Dangerous for almost two years. Sir Persant explains that Ironside could have taken the castle earlier but has deliberately prolonged the siege because he hopes to attract one of the greatest knights in the world: Sir Lancelot, Sir Tristram, Sir Lamorak or Sir Gawain.

The siege is made especially infamous by Ironside’s treatment of defeated challengers. Gareth sees almost forty fully armed knights hanging by their necks from great trees, with their shields, swords and golden spurs still attached. These are knights who came to rescue Lionesse and were defeated and executed by Ironside without mercy.

A great horn made from elephant bone hangs from a sycamore tree near the siege. Any knight who wishes to challenge Ironside must blow it. Dame Lynette warns Gareth that Ironside’s strength increases as the morning advances until, at noon, he possesses the strength of seven men.

Gareth refuses to avoid Ironside at his strongest. He blows the horn, causing the entire siege and castle to ring with its sound. Ironside is armed by his attendants, and everything he bears is blood-red: his armour, shield, spear and horse.

Before the battle begins, Gareth sees Dame Lionesse watching from a castle window and declares that he will fight to rescue her or die. Ironside claims Lionesse as his own lady, but Gareth answers that the siege proves she does not welcome his love or companionship.

Gareth condemns the sight of the hanged knights as a disgrace to knighthood. Ironside attempts to use their bodies as a warning, but Gareth replies that the shameful display gives him greater courage to fight.

The two knights charge with such force that their breastplates, saddle-girths and other equipment break, throwing both men to the earth. They rise and continue on foot, striking one another with swords until pieces of their shields and armour fall across the field.

Their battle continues through noon and into the evening. Both men become exhausted, wounded and covered in blood. Their armour is cut so badly that parts of their bodies are exposed. Ironside is described as a skilful and cunning knight of war whose methods force Gareth to adapt his own fighting.

During an agreed rest, Gareth removes his helmet and sees Lionesse at the window. Her encouragement renews him, and the battle begins again. Ironside then knocks Gareth’s sword from his hand and drives him to the ground.

Lynette cries out that Lionesse is watching and weeping. Gareth recovers, retrieves his sword and attacks with renewed force. He knocks Ironside’s sword away, strikes him to the earth and removes his helmet in preparation to kill him.

Ironside yields and asks for mercy, but Gareth remembers the executed knights and declares that honour will not allow him to save the man responsible for their shameful deaths. Ironside then explains the reason for his actions.

He says that he once loved a lady whose brother had been killed, supposedly by either Sir Lancelot or Sir Gawain. She demanded that Ironside swear an oath to fight until he encountered one of those two knights and to put every defeated knight to a dishonourable death. Ironside accepted the oath and directed his vengeance against Arthur’s fellowship.

This explanation provides Ironside’s motive, but it does not erase his responsibility. Gareth continues to describe his conduct as evil and shameful. Numerous earls, barons and knights kneel and beg Gareth to spare him, arguing that Ironside can make restitution whereas killing him cannot restore the dead.

Gareth finally grants mercy under strict conditions. Ironside must enter Castle Dangerous and submit himself to Dame Lionesse. He must compensate her for the damage done to her lands, present himself before King Arthur and ask forgiveness from Sir Lancelot and Sir Gawain for the hatred he directed towards them.

Ironside accepts every condition, gives Gareth homage and fealty and provides guarantees that the agreement will be fulfilled. He and Gareth remain in the tents for ten days while both recover from their wounds.

Ironside then submits to Lionesse, who accepts him after sufficient guarantees are provided, and the damage caused by the siege is restored. He travels to Arthur’s court and openly places himself at the mercy of Lancelot and Gawain.

At Arthur’s court, Ironside reveals his true name and states that no knight in thirty years had previously defeated him in single combat. He arrives with six hundred knights and promises that they will answer Arthur’s summons. Arthur welcomes his submission but tells him plainly that he must never again behave as a murderer.

Ironside promises to abandon his former customs and kneels before Lancelot and Gawain to ask forgiveness. Arthur offers to honour him and bring him into the Round Table if he remains loyal.

At the wedding of Gareth and Dame Lionesse, Ironside arrives with three hundred knights and performs homage to Gareth. He asks to serve as Gareth’s carver at the feast, and Gareth grants him the office.

Ironside later appears among Arthur’s established knights. He is one of the ten warriors chosen to accompany Queen Guinevere when she rides out for Maying and fights strongly when Sir Meliagrance’s forces attack the queen’s company.

Ironside’s later service does not make the deaths at Castle Dangerous insignificant. His story is one of conditional mercy and enforced restitution: Gareth spares him only after demanding submission, compensation, public accountability, an end to his murderous behaviour and service under Arthur’s authority.