Deirdre was a 15-year-old Celtic princess who lived in North Ireland during the dawn of the Celtic age, around the year 500 BC.
She was the third and youngest daughter of the druid King Gwynwyll, and was said to be very beautiful as she had sandy brown hair, sea green eyes, white cream skin, and lips as red as wild rose. As a result, there was much concern in the tribal community as many other virgins were envious, and many warriors young and old wanted her.
Eventually, her father decided to marry her off to a member of their tribe; one such member was a young deformed teenager named Enda, who was passionately in love with her and asked if he could be the one to marry. However, Deirdre's father laughed at the request and instead betrothed her to a young warrior named Cullain.
However, Enda believed that if he could get to Deirdre and confess his love for her, she would like to marry him instead. When Deirdre went to collect water from the nearby river, Enda followed her, and, when she saw him as he tried to explain his reasons, she became frightened and almost fell into the river. Enda then tried to save her, but she misunderstood his intentions, believing he meant to rape her, and fled.
Unbeknownst to Deirdre, her severe rejection of Enda resulted in him denying his love for her and plotting her murder. Shortly afterwards, during Samhain, she and Cullain were dancing to their engagement when they were both attacked and viciously murdered by Enda, who was then killed by the vengeful tribe moments later.
Deirdre's actions would result in Enda having his soul cursed to wander the Earth until the end of time, repeating her and Cullain's murder on Samhain. It is also implied that she is distantly related to Michael Myers and Laurie Strode.
As with Enda, Deirdre's personality is very complex. She seems to be mean-spirited and unkind, as she treated Enda with revulsion and accused him of trying to rape her.
However, it is highly possible that she was led to believe that he was intending to harm her due to deformed people being considered outcasts back then.
As she was being killed by Enda, she recognized him and saw a sad look in his eyes. This may indicate that she felt remorse for her actions.