Diarmuid Ua Duibhne or Diarmid O'Dyna (also known as Diarmuid of the love spot) is a son of Donn and one of the most famous Fianna's member in the Fenian Cycle of Irish mythology (traditionally set in the 2nd to 4th century). He is most famous as the lover of Gráinne, the intended wife of Fianna leader Fionn mac Cumhaill in The Pursuit of Diarmuid and Gráinne. Aonghus Óg or Aengus is Diarmuid's foster father and protector. Diarmuid is a highly skilled warrior and well-liked and much valued member of the Fianna, he single-handedly slew 3400 warriors in a battle and he saved Fionn and the Fianna.
Aengus owned a deadly sword named Moralltach or Nóralltach, it translates as the great and fierce one, given to him by Manannán mac Lir. In The Pursuit of Diarmuid and Gráinne it is said of Moralltach that it left no stroke nor blow unfinished at the first trial. Aonghus gave this sword to his foster-son Diarmuid, in addition to a sword named Beagalltach, the Little Fury. Along with these two swords, Diarmuid is known to have wielded two spears, Gáe Buidhe ("Yellow Spear") and Gáe Dearg ("Red Spear"), which caused wounds that could not be healed. Diarmuid used Gáe Dearg and Moralltach for adventures which were matters of life and death. Diarmuid also used Gáe Buidhe and Beagalltach for lesser adventures.
Vicious curse His father, Donn, was a warrior of the Fianna. At a dinner party, Donn, feeling jealous because of the attention given to the son of Aengus' steward, killed the steward's son when no one was looking. Aengus resurrected the steward's son in the form of a boar, but the steward still required Fionn to find out the truth and, upon learning the truth, put a curse upon Diarmuid: He was to be killed by the steward's transformed son.
Magical love spot Diarmuid is also famed for his love spot, a birthmark, that makes him irresistible to women. Diarmuid, while hunting one night, met a woman who was the personification of youth. After sleeping with him she put a magical love spot on his right cheek that caused any woman who looked at it to fall in love with him.
Loathly Lady and Cup One freezing winter's night, the Loathly Lady brazenly entered the Fianna lodge, where the warriors had just gone to bed after a hunting expedition. Drenched to the bone, her sodden hair was snarled and knotted. Desperate for warmth and shelter, she knelt beside each warrior and demands a blanket, beginning with their leader Fionn. Despite her rants and temper tantrums, the tired men only rolled over and ignored her in the hope that she would leave. Only young Diarmuid, whose bed was nearest to the fireplace, took pity on the wretched woman, giving her his bed and blanket. The Loathy Lady noticed Diarmuid's love spot and said that she had wandered the world alone for 7 years. Diarmuid reassured her and told her she can sleep all night and he that he would protect her. Towards dawn, he noticed that she had become a beautiful young woman.
The next day, the Loathly Lady rewarded Diarmuid's kindness by offering him his greatest wish—a house overlooking the sea. Overjoyed, Diarmuid asked the woman to live with him. She agreed on one condition: he must promise never to mention how ugly she looked on the night they met. After 3 days together, Diarmuid grew restless. The Loathy Lady offered to watch his greyhound and her new pups while he went hunting. On three separate occasions, Diarmuid’s friends, envious of his good luck, visited the lady and asked for one of the new pups. Each time, she honoured the request. Each time, Diarmuid was angry and asked her how she could repay him so meanly when he overlooked her ugliness the first night they met. On the third mention that he had promised never to speak of, the Loathly Lady and the house disappeared and his beloved greyhound died.
Realizing that his ungratefulness has caused him to lose everything he valued, Diarmuid set out to find his lady. He used an enchanted ship to cross a stormy sea...