In 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 honor, in contrast to the arrogant personality of Kayneth. He shares a bond of mutual respect with rival Servant Saber, his greatest wish being to face her in fair combat.
Lancer is summoned by Kayneth Archibald El-Melloi in the 4th Holy Grail War, who originally intended to summon Rider-class Servant, Iskandar. Because his pupil Waver Velvet stole the artifact he had meant to use as a catalyst, Kayneth summoned Diarmuid Ua Duibhne in Iskandar's stead. Lancer's contract with Kayneth is unique in that, while Kayneth holds the Command Spells, the energy to materialize the Servant is maintained by Sola-Ui, Kayneth's fiancée.
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.
