Lancer (Fate/Zero)

Lancer is the Servant of Kayneth Archibald El-Melloi during the 4th Holy Grail War. Lancer is generally even-tempered, and absolutely loyal to his Master. He is known for his chivalry and sense of honour, in contrast to the arrogant and unsavoury personality of Kayneth. He shares a bond of mutual respect with rival Servant Saber, his greatest wish being to face her in fair combat.

Abilities
Lancer possesses a curse of the Mystic Face variety, not unlike the Mystic Eyes exhibited by Medusa. The curse takes the form of a beauty spot on his face, and causes any woman who looks upon his face to instantly fall in love with Lancer. Like most curses, however, the curse can be overcome by individuals with high magical resistance, such as accomplished magi or certain Servants.

Lancer possesses the exceptional agility and speed of Lancer-class Servants, like Cú Chulainn of the Fifth Holy Grail War.

True Identity
His true identity is Diarmuid Ua Duibhne, the son of Donn, foster son of Aengus Óg and a warrior of the Fianna. Known as Diarmuid of the Love Spot, the appellation resulted from an encounter with Gráinne, a woman who caused a magical love spot to appear on his head. Any woman who looked upon his face would instantly fall in love with him.

Gráinne, the bride of Fionn mac Cumhail, fell in love with Diarmuid when she saw him in the wedding party and subsequently laid a geis upon him so he would run off with her. Their flight from Fionn mac Cumhail was aided by Aengus Óg, who eventually intercedes on their behalf such that Fionn pardons Diarmuid and the couple is allowed to live in peace. The pair settle in Kerry and produce five children.

Years later, Diarmuid is mortally injured when a giant boar gores him on the heath of Benn Ghulbain. Because Fionn, who invited him on the hunt, did not let Diarmuid drink the water from his hands, which had the power to heal, Diarmuid dies.

Role
Lancer is summoned by Kayneth Archibald El-Melloi in the 4th Holy Grail War, who originally intended to summon Rider-class Servant, Iskander. Because his pupil Waver Velvet stole the artifact he had meant to use as a catalyst, Kayneth summoned Diarmuid Ua Duibhne in Iskander's stead. Lancer's contract with Kayneth was unique in that, while Kayneth held the Command Spells, the energy to materialize the Servant was maintained by Sola-Ui, Kayneth's fiancée.

During a mêlée fight with Saber, he attains the upper hand by successfully striking her with Gáe Buidhe, but is interrupted by Iskander. This sets of a sequence of events culminating in the Servant Berserker attacking a weakened Saber. Lancer refuses to fight alongside Berserker, claiming it goes against his code of honour, but is forced to attack Saber when Kayneth activates a Command Spell. He is ordered to back down only after Rider intervenes yet again, forcing Berserker to retreat and threatening to join Saber in finishing off Lancer.

Lancer appears later in Kayneth's base of operations, the Fuyuki Hyatt Hotel, where he is criticized by Kayneth for holding back against Saber. He is spared further verbal abuse by Sola-Ui, who berates Kayneth for not choosing to have Lancer work with Saber to defeat the more dangerous Berserker, and accuses him of cowardice for not actively participating. Lancer forces her to apologizes by stating he will not allow her to reproach his Master. This in turn disturbs Kayneth, who believes that Sola-Ui has become infatuated with Lancer. Before the issue can be addressed, the hotel is attacked by Emiya Kiritsugu and Hisau Maiya, who destroy the hotel's foundation and collapse it around the three.

When Kayneth and the other Masters are offered a reward of extra Command Spells for defeating Caster, Lancer is sent to kill off the magic-wielding Servant, who at the time is engaged in battle with Saber. With Saber's help, he is successful in dispelling Caster's monster army with Gáe Dearg, but abandons his duel with her in order to rescue his Master Kayneth from Emiya Kiritsugu. Rendered bedridden and unable to perform magic, the injured Kayneth is forced to hand over his remaining Command Spells to Sola-Ui, whose infatuation with Lancer has escalated to near-obsession. An uncomfortable Lancer is disturbed by how his current situation resembles his past life, when the betrothed of his then-master Fionn mac Cumhaill fell in love with him, with dire consequences.

Lancer plays a key role in defeating Caster, when the Servant summons a giant monster to wreak havoc on Fuyuki City. He willingly destroys Gáe Buidhe in order to remove the enchantment inhibiting Saber's abilities, allowing her to employ her full power and destroy Caster. Saber and Irisviel von Einzbern would later confront Lancer to finish his duel with Saber, but both are unaware that Saber's Master, Emiya Kiritsugu, had already formulated a plan to eliminate both Lancer and his Master. The battle ends when Kiritsugu, holding Sola-Ui hostage, coerces Kayneth into using his last Command Spell; Lancer is thus forced to drive Gáe Buidhe into his own chest. The shocked Servant realises that he has been fatally betrayed by his current Master, just as his former master Fionn caused his death during his first lifetime. Enraged, Lancer dies cursing the Holy Grail, Saber, Kiritsugu, and the world at large for his fate.