Portrayed by Madelaine Petsch
Full Name Theresa Rourke Cassidy
Age 25
Height 5'7"
Build Athletic
Eyes Green
Hair Red
Skin Caucasion



Theresa Cassidy is known as the daughter of Banshee, Sean Cassidy, as well as known to have associations with an international criminal, but she has never been properly identified nor prosecuted.


It began as a competition to see who could capture the heart of one Maeve Rourke, a lovely Irish woman that had eyes for only Sean. Two cousin's hatred for each other would be deepened, as Sean and Maeve eventually married. Unfortunately, Sean was sent off on a secret mission for Interpol never knowing that Maeve was already pregnant with their daughter.

While Sean was still away, Maeve had their daughter, Theresa. On a fateful afternoon, Maeve took her infant daughter with her on a visit to Armagh in Northern Ireland. While Maeve was there, (an innocent bystander) she was killed by an explosion caused by terrorists. No trace of Theresa was found by the authorities and it was assumed that she had been killed, as well. However, Terry's uncle Tom had been present at the scene of the explosion and had secretly carried the young infant off with him. Tom suspected that Theresa may have powers like her father, and thus desired to not only hurt Sean, but use those powers for his own schemes.

Sean, upon learning of his wife's death and never knowing that he had a daughter, was filled with grief. The Irishman went further into his career and didn't return to the Keep for many, many years afterwards.

During her young life, Theresa was placed in private schools, constantly shipped off so she wouldn't be involved with Tom's criminal activities until she could be an asset instead of a problem. Theresa never truly felt at home, knowing her Uncle was a 'criminal', living with that guilt, as well as never actually gaining the love and support she needed to live, she went into the bottle very, very early in her young life. To this day, she has a problem with alcohol, as well as truly giving her trust easily to anyone.

Eventually, Uncle Tom was reunited with an old associate. It was Cassidy that suggested this associate of his, and Tom, form a partnership for criminal activities, a partnership that proved quite profitable to both ever since. Theresa, after turning into an adolescent with her sonic abilities, was forced into helping Tom and his friend. On one of her first outings she encountered a local hero, which she was able to initially defeat. Though only initially, for after gaining the help of the X-Men, Tom's associates and Theresa were defeated.

It was soon after this, that Tom, compassionately, decided the life of a criminal was not for Siryn, and thus, sent a letter along with a startled Theresa to the X-Men. It was only then that Sean found out that Theresa was his daughter, a tearful reunion, as father and daughter had found each other at last.

When Sean went to Muir Island, Theresa went with him. She spent quite awhile there, but her inability to get close to anyone caused her to finally leave the island and strike out on her own.

Theresa went through many adventures, and team-ups over the past several years, though recently she has decided to get out of the adventuring career and start a simple life a a florist. She's taken out a loan, set up a shop, and is attempting that 'independent' lifestyle.

Character Details

Theresa has not had an easy life. Her mother was murdered when Theresa was just a small baby. She was raised by an 'uncle' who did not really care about Theresa's well being, but only that she could one day be a tool, an instrument against his cousin, Sean. She was sent from boarding school, to boarding school, always in motion, and never given anything more than a good education and an empty house to live in. As a result, Theresa was not exactly an exemplary student, and she took to drinking very easily.

Thus much of Theresa's personality revolves around her emotions. She's quick to feel anything - whether it's happiness or anger. She makes friends easily enough, but true trust comes very rarely, if at all. She has never allowed herself to get close to anyone, not so much as a fear of them hurting her, but of her hurting them.

She's got a very quick temper that lasts a very long time. At times, she can be down right temperamental or angry for no apparent reason at all. A slight against Theresa tends to last a very long time.

She has a lot of issues that can be worked through, but Theresa's stubborn personality will not let that happen. Her father and her are at least on talking terms, but anything closer is not an easy thing to come by. After all, they both are very much the same when it comes to attachments.

In times of need, Theresa can be level-headed and a cool under fire leader, just as long as she isn't drinking, or the person she's fighting isn't her uncle.


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