Theresa Cassidy was born to Sean Cassidy, the first Banshee, and Maeve Rourke while Sean was away on a mission for INTERPOL. Not long after Theresa's birth, Maeve was killed by a bomb blast and young Theresa was taken in and cared for by her uncle, Thomas Cassidy, a.k.a. Black Tom. When Sean finally returned home from his mission to find Maeve dead, he directed his anger toward his brother, Tom, for not looking after her, attacking him and breaking his leg. Out of spite, Tom never told Sean about his daughter, allowing Sean to believe that Theresa had died with her mother.
Tom decided to raise his niece on his own. As time went by, Tom became involved in increasingly dangerous criminal activities and, for her protection, shipped the twelve-year-old Theresa off to St. Elizabeth's Boarding School. When she was fifteen, she found out that Black Tom had been arrested by Interpol agents. After Theresa developed her mutant abilities -- a sonic scream, the same as her true father's--she joined her uncle in his life of crime under the moniker Siryn. She would eventually discover the truth of her origin, however, and become a hero.
