Diarmuid Ua Duibhne is a heroic Lancer-class Servant in Fate/Zero, summoned by Kayneth El-Melloi Archibald for the Fourth Holy Grail War. Based on the legendary Irish warrior of the Fianna, he is admired for his loyalty, chivalry, and tragic beauty. In the series, he serves as a noble and highly skilled frontline fighter, wielding his twin spears with exceptional precision. His role is marked by honor, sorrow, and the conflict between duty and the personal code of a true knight.