BIOGRAPHY - Page 1
The Lord Thomas Samuel Eamon Cassidy was born to be a scoundrel. One of the heirs of Cassidy Keep in County Mayo, Ireland, he and his younger cousin Sean were the sole surviving members of their clan by their late teens, masters of the manor but nearly penniless otherwise. As close as brothers during their upbringing, Tom and Sean apparently discovered their mutant abilities together. Tom still differed from Sean in many ways, though. He was educated at Oxford University, becoming more of a "man of the world" than his younger, rougher cousin. "Black Tom" Cassidy was also more of a playboy and a womanizer, a gambler who played fast and loose with what remained of their family fortunes.
A wedge began to develop between the cousins one night when Sean brought home a university 
girl and daredevil motorcyclist named Maeve Rourke. Maeve saved Sean from a suspicious and prejudiced English copper as Sean was hitching home from a concert in Northern Ireland. Sean in turn saved her when the officer shot out their tires at the side of a cliff, flying them both back to Cassidy Keep using his sonic scream. Tom and Sean were equally enchanted with Maeve during her visit, and they both began courting Maeve from that point on. The competition was friendly but serious between the cousins, as Maeve seemed genuinely affectionate towards both of them.
The competition for Maeve's feelings came to an end the night of her university dance, where Sean was due to escort her. The English policeman had tracked Sean down and ran him off the road on his way to the dance. Sean returned to Cassidy Keep, seriously (but not fatally) wounded. As his wounds were tended to by the household staff, Sean insisted Tom go on in his place so Maeve was not left unescorted. Tom eagerly agreed and he arrived at Maeve's door, making no excuse for Sean's absence and leaving Maeve to believe Sean stood her up. During the dance, however, Tom recognized just how upset Maeve was at Sean "abandoning" her, and gave in to his better nature. Tom admitted the truth to Maeve about Sean's injuries and encouraged her to go to him, knowing he was losing her in the process. When he asked Maeve if she hated him for lying, she surprised Tom by appreciating how he put her feelings over his own, and declared she was his friend for life. [Classic X-Men #16]
Tom did try his best to abide the love between Sean and Maeve. He even stood as Sean's best man at their wedding. Still, Tom was hurt deeply by losing Maeve to Sean. In his mind, he tried to justify her decision by proving she was right to reject him, leaning into his reputation as "Black Tom" Cassidy more than ever before. It was here that Tom truly began his criminal career, getting involved in darker dealings than his previous playboy days ever allowed.
It didn't help that Sean joined Interpol and was frequently away from Cassidy Keep for long stretches of time, leaving Tom alone with the woman who didn't choose him. Tragically, Maeve died in a terrorist bombing while Sean was away at work, just after giving birth to their daughter. Sean was out of touch completely while on his missions and didn't return home until months after Maeve had died. Meanwhile, those friends and family who knew of Maeve's child believed the girl died in the same bombing. In fact, baby Theresa was being cared for by Tom.
Tom met Sean at Maeve's grave site when he returned, planning to tell his cousin about his newborn daughter, hoping to give him a glimmer of good news. Before he could, however, the 
distraught Sean lashed out at Tom, blaming him for not keeping Maeve safe while he was away. Although Sean's sonic scream could not hurt Tom directly, it tore up the ground under his feet and sent Tom on a nasty fall. Tom broke his leg in the incident and could never walk right again without the use of a cane. Sean flew off immediately after their confrontation, throwing himself back into his work in his grief.
Wounded physically and emotionally by his cousin, Black Tom decided Sean was dead to him from that point onwards, and resolved never to tell him about his daughter, Theresa. Black Tom became even blacker after that, turning to crime as his primary means of support. He loved Theresa as he raised her, but there was always an unspoken bitterness between them as Tom 
never told her anything about her father. Theresa was away at private school when Sean finally returned to Cassidy Keep and reconnected with his cousin. Even this turned out to be a betrayal in Tom's eyes, for Sean was actually undercover on assignment from Interpol, investigating the jewel thefts, black marketeering and other crimes for which Black Tom was responsible. Sean arrested his cousin, and Black Tom was sent away to prison for years.
While incarcerated, Tom met Cain Marko, the human Juggernaut who frequently clashed with the X-Men. Black Tom and Juggernaut bonded over their criminal proclivities and intense hatred for their cousin and stepbrother, respectively. This bond became even clearer once word reached Tom that Sean had become a member of the X-Men as Banshee. [X-Force (1st series) #31, 91]
[Note: Reports from the above two issues are somewhat ambiguous and contradictory about how Tom kept Theresa's existence a secret from Sean. Theresa apparently grew up with friends and family from County Mayo, but why none of them ever told Sean about her is unclear. One report suggested Tom openly claimed Theresa as his illegitimate daughter and Sean even knew about her, although clearly they never met. Basically, any explanation has to lean heavily on the extreme isolation of Cassidy Keep and Sean's deliberate absence from home after Maeve's death to make the story remotely credible.]
Black Tom and Juggernaut escaped from prison with the assistance of Davan Shikari, the Shi'ar agent known as Eric the Red. He wanted Charles Xavier eliminated before the renegade princess Lilandra could recruit Xavier in her struggle against her mad brother, the Emperor D'Ken. Black Tom and Juggernaut eagerly accepted payment to go after their hated relatives. Tom decided to 
set a trap for Xavier, Banshee and the X-Men at Cassidy Keep. He and Juggernaut took possession of the castle, imprisoning the family of the steward Eamon O'Donnell to force him into compliance. A number of advanced deathtraps and weapons were installed in the castle over several weeks as preparations were made. Eamon attempted to get word out to Sean Cassidy through the family barrister Flaherty, but the lawyer misunderstood the extent of the threat and thought Black Tom was merely trying to seize Sean's inheritance of Cassidy Keep. He sent a letter to New York, inviting Sean to visit and claim his inheritance just before Black Tom caught Flaherty and bio-blasted him. [X-Men (1st series) #99]
[Note: It is somewhat uncertain who is the rightful lord by birth of Cassidy Keep, Tom or Sean. Nothing is known about the generation preceding them. In X-Men #101, Sean claimed Flaherty's letter indicated he had "just inherited Cassidy Keep," which would usually indicate the current lord had just died, or their estate was finalized, although Sean didn't indicate a relative had passed. Perhaps Tom was forced to abdicate with his arrest and the paperwork took years to establish Sean's claim. An explanation in the Marvel Handbooks is that Tom lost Cassidy Keep to Sean in a poker game, although this claim seems dubious and is not supported by the comics themselves.]
Forced to step up their timetable, Black Tom and Juggernaut prepared to ambush Banshee and the X-Men when they arrived at Cassidy Keep for a vacation. Eamon O'Donnell was forced to welcome the X-Men without warning them, due to his own family's peril. As Banshee and the X-Men proceeded to the dining hall, they were caught in a trap door that carried them into the dungeons where Black Tom and Juggernaut awaited them. Cain Marko occupied most of the X-Men, while Black Tom sought revenge on his cousin. Banshee and Black Tom had a running duel 
through Cassidy Keep with their fists, swords and axes, taking out years of frustration on each other. The tide turned against the villains when a hole to the outside was blasted in the dungeon, freeing the claustrophobic Storm to regain her senses and fight back. Banshee and Black Tom finally ended their fighting on the ramparts of the castle, when Sean flipped Tom and tossed him over the side to the seas below. Juggernaut dove after his partner and the fighting was ended. [X-Men (1st series) #101-103]
Juggernaut apparently succeeded in rescuing Black Tom from the surf, for they soon returned to their mercenary lifestyle. Cain wanted immediately to seek revenge on the X-Men, but Tom counseled him to try a different tactic for once. Instead of barging into the X-Mansion themselves, Black Tom and Juggernaut hired the elite assassin known as Arcade to eliminate the X-Men for them, while they returned to paying mercenary jobs in the meantime. [X-Men (1st series) #122]
By this time, Tom had reconnected with Theresa and learned of her mutant sonic abilities, similar to her father's. Seeing an opportunity for profit and to share his life with his adopted daughter, Black Tom gave her a costume and new identity as Siryn, bringing Theresa along on thefts and other jobs he pulled with Juggernaut. [X-Force (1st series) #91]
In San Francisco, Black Tom, Juggernaut and Siryn planned to attack the federal mint and steal America's supply of Vibranium. The rare and precious ore could then be ransomed back to the United States or sold to foreign powers, whoever paid better. Siryn used her sonic scream to trigger bank and burglar alarms throughout the city, sending the authorities rushing to false calls and the mint free for pillaging. Unfortunately for them, the Bay area had a new super-heroine named Spider-Woman, whose enhanced hearing pinpointed Theresa's location. Spider-Woman attacked the burglars but was overpowered by Black Tom and his crew, and left to take the blame with the police. [Spider-Woman (1st series) #37]
The X-Men had detected Black Tom and Siryn on Cerebro, and found themselves allied with Spider-Woman against the criminals. Storm, Angel and Colossus joined Spider-Woman in tracking down Black Tom's hideout, and the battle ultimately turned out in favor of the heroes. Black Tom lashed out at the X-Men for the injuries Theresa suffered in the fight while they were being taken into custody, but Spider-Woman easily retorted that Tom was responsible for putting her in the criminal 
lifestyle in the first place. Black Tom conceded the point, and dramatically declared Siryn and Spider-Woman completely innocent of his misdeeds while preparing a letter to Sean, revealing the existence of his cousin's daughter to him. Tom would call this an act of gallantry if asked but, with the X-Men on the scene, it was inevitable Banshee would learn of Siryn anyway. In truth, Black Tom Cassidy was taking control of the situation the only way left to him, disassociating himself from Theresa by choice before she abandoned him for lying about her father for her entire life. [Spider-Woman (1st series) #38, Uncanny X-Men (1st series) #148]
Black Tom Cassidy and Juggernaut were soon free again and continued their criminal activities, building a rather sizeable fortune. They often operated out of a computer-guided pleasure yacht as they moved between jobs. Tom counseled Cain on thinking through their missions more than just lumbering forward. He convinced Juggernaut to break apart and reshape his helmet, creating a smaller helm with a second skullcap underneath, doubling his resistance to telepathic attacks. Tom also had the idea of recruiting the reclusive psychic known as Madame Web to guide their endeavors. Not having enough information about the woman to make her an offer, Tom agreed to just send Cain directly to retrieve her by force. Unfortunately, Spider-Man became involved in the caper and Juggernaut was trapped in a pool of wet cement. It was months before Black Tom's partner dug himself out. [Amazing Spider-Man (1st series) #229-230]
Feeling responsible for the failure, Juggernaut decided to get Tom something special for his birthday. He returned to the Temple of Cyttorak in Korea and recovered the Ruby Gem that gave Cain Marko the power of Juggernaut. Back in New York, he presented the ruby to Tom at 
his party without explanation, causing Tom to spontaneously assume the proportions of the Juggernaut. Black Tom was shocked at his transformation and so were the affectionate women at the party, who fled. Tom's ungratefulness at Cain's gift of sharing his power led to a fight between the two of them, which drew the attention of Spider-Man and the X-Men.
Once Tom managed to calm down, he recognized the sheer power at his fingertips now, and made peace with Cain. Fortunately for the heroes, Tom and Cain only had half of Cain's original might apiece, instead of two Juggernauts at the peak of their power. The power was also unstable when shared between hosts -- when Rogue temporarily stole Black Tom's power with her touch, it returned to the ruby and not to Tom after her period of power ended. Juggernaut reclaimed the ruby and his full power at the battle's end, tossing the gem into orbit so no one could steal his power again. As they escaped through the sewers, Black Tom sincerely thanked Juggernaut for a fantastic birthday. It 
had been a wonderful donnybrook with no harm done (to them, at least), and Tom got the chance to walk in Cain's shoes and understand him better, which was a fine gift after all. [Marvel Team-Up (1st series) #150]
On another occasion, Black Tom dispatched Juggernaut to cause a ruckus in Edinburgh, Scotland. Cain succeeded in not only causing chaos, but also drawing the attention of the X-Men in a massive battle. In the meantime, Tom was looting the Bank of Scotland, making off with a sizeable payday. [Uncanny X-Men (1st series) #218] Cain was captured by the X-Men, however, and held by Scotland for some time. While he eventually escaped, Juggernaut operated independently until being banished to an extra-dimensional void while fighting Thor. Black Tom Cassidy was forced to operate alone during this period, but was determined to find his friend and somehow bring him home.