I know Irish women can be load but lady takes the cake. Introduced (as a villain) in Spider-Woman #37 (1980) by Chris Claremont and Steve Leialoha, Theresa is the daughter of Sean Cassidy and his wife Maeve. She was born when Sean was deep undercover for Interpol, unaware that Maeve was pregnant. Shortly after Theresa’s birth, Maeve was killed in an IRA bombing. The child was taken in by Sean’s cousin, Tom, who kept the truth about her from Sean out of spite as he loved Maeve too. As her powers developed, Black Tom began having her help with his crime. She first came to the notice of the X-men when Black Tom and herself battled Spider-woman and the X-men, with her having taken the codename Siryn. The pair were arrested but Black Tom took all the blame, allowing Siryn to be exonerated. He wrote to Sean and told him the truth about who she was. The father and daughter were reunited and would begin living together in the Cassidy Keep, along with Moira MacTaggart.

While helping on Muir Island, she would meet Jamie Madrox, Multiple Man, and would begin a relationship. The pair would later search for an escaped Sunspot and would join the Fallen Angels. She would later join the X-Force when she learnt that Black Tom and Juggernaut planned to bomb the World Trade Center. She would become the Deputy Leader of the team under Cannonball. She would later meet Deadpool and the pair would develop feelings for each other but parted on good terms. After a bout of alcoholism, Theresa would eventually lose her voice and powers. She recovered when Deadpool kidnapped her and used Wolverine healing factor for help her, which they didn’t like. She would later join her father’s X-Corps.

After M-Day, she would X-factor Investigations. One drunken night resulted in her getting pregnant with Madrox’s dupe’s child. She asked him to marry him, and he accepted. However, after giving birth to their son Sean, it was revealed that the baby was a dupe of Madrox. Madrox left the team in sorrow and Siryn took over leadership but soon disbanded it. Monet took her home to the Cassidy Keep, hoping that it would help her recover from the loss of her son. Meeting another dupe of Madrox who was a reverend, he helped her recover from the loss of her baby and the death of her father and she took the name Banshee. She would return to New York and reconciled with Madrox and rejoined the team.

After Havok and Polaris took over the team, Siryn contacted the goddess Morrigan to help Polaris mental state. Morrigan explained to Theresa that the role of the goddess is one that is one to be passed on and she wanted a break from it. Theresa agreed to take on the role and killed the Morrigan. She was transformed into the newest Morrigan. She was later freed from the role and joined the rest of mutant kind on Krakoa. She would join the X-Factors team.

Siryn is quite a popular character for those that read the X-force and Deadpool titles. She is one of the few Irish superheroes in Marvel. With Hasbro push to complete the X-force team, we knew she was coming, which she is in the X-men Bonebreaker wave.