The chances are he has covert narcissistic personality traits (I couldn't say if he is a narcissist or not - I'm just making the point that these are characterestics) - they key defining factor of which is an inability to take responsibility or accountability. This translates often into a sort of weirdly disordered thinking - the person is very unhappy but feels they are the victim, refuse to seek help and, often, have long and complex reasons why they have been treated badly which, when you break them down, are completely batshit crazy.
The sad truth it is this vulnerability and genuine unhappiness that they also use to control and manipulate people. I don't even think they do it on purpose most of the time. I know one like this.. I loathe him for a million reasons but I also feel sorry for him becuase I know that he genuinely thinks that we all hate him because we are terrible people and his life has been ruined because he was part of our family for a while.
so, for example, the physical abuse, even if the person says something like, "I know I shouldn't", it's followed by "but" ... "but I didn't know what else to do " "but my world was crashing down on me" "but my mental health is and was so terrible I wasn't in control".
Also, I'm sorry to say he will never be a positive version in his children's lives. Fo ra start, he is a physically violent man so that's always going to be a problem. More relevant, even if he stays in touch with them, he will shift his victim mentality to them. These are the people who are outraged that their 15 year old isn't calling them weekly or who will tell their children that they could have done x or y, but couldn't because they had children or because of the children's mother or whatever.