Published March 17, 2022

The Cassidy Family History

A spotlight on the mutant family of Banshee, Siryn, and Black Tom!

To mark St. Patrick’s Day, we look back at the history of Marvel’s favorite Irish mutant family—the Cassidys! This complicated clan have ties that stretch all the way to the early days of the X-Men. Early, early. UNCANNY X-MEN (1963) #28 introduced Sean Cassidy as the sonic screamer Banshee, while his cousin, the energy-manipulating Black Tom Cassidy, followed in UNNCANNY X-MEN #99. Sean’s daughter Theresa Cassidy, (later known as Siryn), would make her debut in SPIDER-WOMAN (1978) #37, showcasing the same flight and sonic screaming abilities as her dad.

The Cassidy family haven’t always been on the same page. Far from it. Sean and Black Tom have an epic rivalry dating back to childhood, further complicated by Sean’s inheritance over a sprawling family estate. But the move to Living Island Krakoa in the recent line of X-Men comics provides a second chance for all mutants. Krakoa has already allowed Sean and Theresa to cheat death. And, for Black Tom and his secondary plant-based powers, anything is possible in Krakoa’s organic landscape. Read this week’s X-MEN UNLIMITED INFINITY COMIC #26 in the Marvel Unlimited app now to keep up with the Cassidys, and take a trip down memory lane with this family ledger of comic moments.


Sean and Tom Cassidy have rarely agreed on anything, but there was one person who united them. Her name was Maeve Rourke, and she was the love of Sean’s life. Tom’s too, (although his love for her was more one-sided even while they dated). Regardless, Tom was Sean’s best man at his wedding to Maeve. Tom did that despite being heartbroken over losing the love of his life for good.

Perhaps the family could have moved past that. Unfortunately, Maeve was killed in a terrorist bombing while Sean was undercover on an assignment for Interpol during his service as an agent. X-FORCE (1991) #31 finally revealed what happened when Sean returned home months later. Sean blamed Tom for being unable to protect Maeve, even unleashing his sonic scream at Maeve’s grave site which badly injured Tom’s leg and left him with a limp for most of his life. The irony is that until Sean lashed out at him, Tom actually planned to tell him about his surviving daughter, Theresa.

Maeve’s tragic history in X-FORCE (1991) #31.
Maeve’s tragic history in X-FORCE (1991) #31.


In the aftermath of Jean Grey’s transformation into the Phoenix, Charles Xavier sent the team on a holiday in UNCANNY X-MEN #101-103. At Sean’s suggestion, Wolverine, Colossus, Storm, and Nightcrawler accompanied him to Cassidy Keep, his ancestral home in Ireland. It’s a magical place, with literal leprechauns and fairies who live there alongside the keeper of the estate, Eamon O'Donnell. During the X-Men’s first visit, Black Tom and Juggernaut took some of the leprechauns hostage and ambushed the X-Men. However, the leprechauns proved their worth by helping the X-Men to escape and turn the tables on their captors.

The magnificent Cassidy Keep castle in UNCANNY X-MEN (1963) #101.
The magnificent Cassidy Keep castle in UNCANNY X-MEN (1963) #101.


Theresa Cassidy was Tom’s trump card against his cousin Sean, but also a way of keeping a part of Maeve for himself. As shown in X-FORCE #31 and issue #91, Black Tom raised Theresa like she was his own daughter, although she called him “uncle” instead of “cousin” or “father.” And, she briefly followed in Black Tom’s footsteps when she was coerced into his life of crime in SPIDER-WOMAN (1978) #37-38.


Black Tom may be a rogue and a scoundrel, but there have been moments where his better nature has made itself known. Case in point: UNCANNY X-MEN #148 featured the first-ever meeting between Sean and Theresa. And it was all set up by Tom (from behind bars). After his capture in the pages of SPIDER-WOMAN, Tom wrote a letter to Sean that explained who Theresa was, and Sean happily accepted his daughter into his life. Theresa and Sean even shared the same mutant powers, strengthening their newfound bond.

Theresa and Sean reunited in UNCANNY X-MEN (1963) #148.
UNCANNY X-MEN (1963) #148


Sadly, Black Tom’s favor wasn’t exactly him turning over a new leaf. In fact, he embraced the life of a villain even more enthusiastically alongside his toxic best friend, Juggernaut. That’s why Theresa confronted the duo in X-FORCE (1991) #4 when they planned a (very) destructive act in New York City. That’s also where she met Cable and X-Force for the first time, ultimately becoming a valued member of the team.

Months later, in X-FORCE #31, Theresa was struggling with her mental health when she traveled home to Cassidy Keep to confront Tom over their shared trauma. By that time, Tom’s physical and mental condition were rapidly deteriorating. At the grave of Theresa’s mother, she convinced Tom to turn himself in and rehabilitate. That was also the moment she resolved to embrace sobriety, but only after she reaffirmed her love for the man who raised her.

Theresa confronts her "uncle" in X-FORCE (1991) #31.
X-FORCE (1991) #31


Following the end of GENERATION X (1994), Sean hit a rough patch. Mystique slashed Sean’s throat and left him for dead in UNCANNY X-MEN #406. That lingering injury severely limited Sean’s power, and led to his actual death in X-MEN: DEADLY GENESIS #2 following his rescue of a plane full of passengers.

Cyclops broke the news to Theresa in X-FACTOR (2005) #7, and she was in serious denial about her dad’s fate. To be fair, death was a fairly temporary condition in the Marvel Universe even before the Resurrection Protocols on Krakoa. That said, Theresa refused to acknowledge that Sean was really gone for a prolonged period, and it led to her emotional and physical decline.

The death of Banshee in X-MEN: DEADLY GENESIS (2005) #2.
The death of Banshee in X-MEN: DEADLY GENESIS (2005) #2.


For a while, Theresa got her life back on track despite carrying an enormous amount of grief. She formed a relationship with mutant detective Jamie Madrox, the Multiple Man, and she even proposed to him when she was pregnant with their child. In X-FACTOR (2005) #39, Theresa gave birth to a healthy baby boy whom she named after her late father, Sean. Tragedy struck soon after, when Jamie picked up his son and absorbed the infant into himself.

That revealed that the Jamie who fathered a baby with Theresa was actually a duplicate, and, by default, their son was a duplicate too. Once Jamie touched baby Sean, there was no way to bring him back. That ended their romance for good, and sent Theresa spinning into a spiral of depression.


After rebuilding her life bit by bit, Theresa took on the Banshee codename in honor of her father and remained a member of X-Factor. She even reconciled with Madrox, even though the love they once had was gone. But when Theresa’s friend and teammate, Polaris, was on the verge of losing her mind, Theresa struck a deal with the god-being entity known as the Morrigan. In X-FACTOR #244, Theresa agreed to kill the previous Morrigan host and assume her mantle and powers so that she could save Polaris’ sanity. This also turned Theresa into a god, and she left the team shortly after.

Theresa Cassidy becomes the all-new Morrigan in X-FACTOR (2005) #244.
Theresa Cassidy becomes the new host of the Morrigan in X-FACTOR (2005) #244.


It turns out that Theresa was right all along—Sean Cassidy just couldn’t stay dead. He was resurrected (and killed again) no less than three times following his original demise. His first return came in the “Necrosha” storyline as an unwilling slave of the Black Queen, Selene. Banshee and a few other dead X-Men returned during the CHAOS WAR, and they managed to save the world before returning to the afterlife. The Apocalypse Twins raised Banshee once more in UNCANNY AVENGERS (2012) #9 as one of their new Horsemen. This left Banshee in a withered and decayed state even after he was freed from their influence. Several months later, Banshee rejoined the X-Men before sacrificing himself (yet again) in UNCANNY X-MEN (2018) #21.


As seen in HOUSE OF X #6, both Sean and Theresa were restored to their previous forms and powers, and happily living life on Krakoa. Even Black Tom found a new lease on life in X-FORCE (2019) #1, as his modified powers gave him an affinity for Krakoa and its complex ecosystem. For perhaps the first time in his life, Black Tom was truly accepted by his fellow mutants and he played a key role in keeping Krakoa and its citizens safe from outside attacks.

As for Sean, he was one of the mutants up for election to join the latest team of X-Men during the inaugural Hellfire Gala event. (Polaris won.) He now appears as a member of the SECRET X-MEN alongside several other ex-candidates. But if the horrifying events of X DEATHS OF WOLVERINE #4 are any indication, then Sean is going to need another resurrection from the Five. His former lover, Moira MacTaggert, just murdered Sean and used his skin to sneak past Krakoa’s defenses. Guess this means they’re never getting back together!

The murder most foul in X DEATHS OF WOLVERINE (2022) #4.


Turns out, the Morrigan wasn’t willing to let go of Theresa so easily. In series X-FACTOR (2020), the Morrigan forced Theresa to die again and again as part of a dark bargain to prevent a massacre on Krakoa. The Morrigan wanted to commit mass murder, but Theresa convinced the god-being to take those urges out on her, the host, instead... for a thousand times or more. Unwilling to see their friend suffer, the new X-Factor team confronted the Morrigan and finally freed Theresa from her grasp.


Marvel Unlimited app-exclusive X-MEN UNLIMITED INFINITY COMIC #26 marks another turning point in the history of Clan Cassidy. For the first time in years, Sean, Black Tom, and Theresa are all reunited at Cassidy Keep on the Emerald Isle. The old conflict between Sean and Tom led to another fight, but this time the outcome is different. With Theresa there to set them straight, Sean finally makes a conciliatory gesture to his cousin, and Tom accepts it. They go out for a night on the town as they had years ago, before all of their troubles began.

Theresa takes over Cassidy Keep in X-MEN UNLIMITED INFINITY COMIC #26.

It’s not a happy ending, because nothing truly ends in the Marvel Universe. But it is a happy present. And at long last, the Cassidys are back together.

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