The Punisher, or Frank Castle, was a normal guy with a family. His military background gave him a set of skills that were both useful and deadly. Once his family was massacred, he snapped. He turned his skills towards punishing those who he thought deserved it. His origin story is one of tragedy and a thirst for justice outside the normal bounds. He doesn't wear a colorful costume like some superheroes. Instead, he has a simple skull emblem on his chest, representing death to those who do wrong.
In the comics, the Punisher isn't simply heartless. His actions are a result of his traumatic past and a determination to fight crime by any means necessary. It's a mix of passion and a warped sense of morality.
I don't think there was a character named Karen in Punisher comics. Usually, the main characters and well-known ones are pretty distinct, and I haven't come across a Karen in this series.
It was the tragic event of his family's death that pushed The Punisher to use extreme methods. Frank Castle had a deep sense of right and wrong. When the mob took away his family, the system didn't seem to be able to hold the criminals accountable in the way he thought they should be. So, he decided to use his military training and his own brand of justice. He saw himself as the only one who could truly punish those who committed such heinous crimes against his family. He's not interested in rehabilitation like the legal system might be; he wants pure retribution.
In some fanfictions, the Punisher may develop a sense of camaraderie with Batman. This would be a big change as he is usually a lone wolf. But through shared battles and mutual respect for their skills, he could start to rely on Batman and be more open to teamwork, which is a significant shift from his character's normal solitary nature.
One popular crossover is with Daredevil. Since they both operate in the darker corners of the Marvel universe in Hell's Kitchen, it makes for an interesting blend. Their moral compasses, while similar in some ways, also have distinct differences. Another is a crossover with the Punisher and Wolverine. The combination of the Punisher's military tactics and Wolverine's berserker rage and healing factor can lead to some intense and action - packed stories. There are also crossovers with characters like Jessica Jones, where the contrast between her more private detective style and the Punisher's all - out war on crime creates great story potential.