Deirdre was a Celtic teenager from the novelization of the first movie.
Deirdre was a 15 year old Celtic princess who lived in North Ireland during the dawn of the Celtic age presumably during 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 it caused much concern in the tribal community as many other virgins were jealous with envy and many young and old warriors wanted her,
Eventually her father decided to marry her off to a member of the tribe, one such member was a young deformed teenager named Enda who was passionately in love with her 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 if he could get to Deirdre and confess his love for her then she would like to marry him instead, however when Deirdre went to collect water from the nearby river Enda followed her and when she saw him as he tried to explain his reason she became frighten and almost fell into the river, Enda then tried to save her but she misunderstood his intentions and believed that he meant to rape her and fled.
Unbeknownst to Deirdre her severe humiliation of Enda resulted in him losing his love for her and plotting her murdered, shortly afterwards on 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 Cullains murder on Samhain, it is also implied that she is Michael Myers and Laurie Strode's ancestor.
As with Enda, Deirdre's personality is very complex. She seems to be a mean spirited and unkind personality as she treated Enda with revulsion and accused him of trying to rape her.
However it is highly possible that she was lead to believe that Enda was intending to harm her due to deformed people being treated as outcast back then.
When Enda murdered her she recognized him and saw the look in his eyes, this may indicate that she had remorse for her actions.