Jon Bernthal had an in-depth interview about The Punisher's "dark headspace" he had to master and the nature of the personage Frank Castle.
According to the interview posted by Marvel, Bernthal declared that a dark headspace is not new to him since he already had some experience with it in other characters he played previously. Each character is different so each one requires its own method to get involved in and its own process.
The actor also declared that being a father of young kids is a real game changer for him. He is grateful for this opportunity to get to play this role after himself became a father. The trauma of the character is very impressive. For Bernthal is essential to understand what would mean to fail your family and lose it on your watch in order to play the part.
The actor has also touched in his interview upon the complicated relationship between Matt Murdock (Charlie Cox) and Castle in "Daredevil" season 2. He explained that in his opinion what makes the "Daredevil" season 2 show so special is what Charlie has done with Matt. This is highly unique rather than just being another "guy playing just another super hero".
Charlie is a fully nuanced, fully realized character. Bernthal explained that in his opinion this is also what needs to be done with the character Frank Castle as well. Both Charlie and Castle have gone through some trauma in their lives and as consequence they are out for justice in their own very different and unique ways. Matt Murdock and Frank Castle are two characters so alike and so different in the same time. They learn from each other when they collide.
According to Screen Rant, the Punisher made his debut back in the pages of the issue 129 of "The Amazing Spider-Man". He was the villain portrayed as an assassin and throughout the years those dark origins kept staying with the character in all live action incarnations as well as in comic books and cartoons.
