The church of scientology has dealt with many high profile defectors. But the father of the undisputed leader of the church quitting, leaving the church and having a war within scientology's ruling... See More
The church of scientology has dealt with many high profile defectors. But the father of the undisputed leader of the church quitting, leaving the church and having a war within scientology's ruling family. I have never met a more competent and more intelligent and more tolerant, more compassionate being. That is how Tom cruise describes David miscavige, the unquestioned leader of scientology, one of the most controversial new religions on the planet. It's a story that affects every scientologist. Reporter: Within the church, he's exalted. Thank you. It's my pleasure. Reporter: He rubs shoulders with celebrities such as cruise, John travolta and others. Among some former members he's wildly controversial. He uses that power to hurt people. We were hoping to talk to David miscavige if he's here today. I don't think that's possible. Today he's busy. Reporter: Miscavige is famously press shy. It's not cool to be set up here this afternoon. Reporter: His live television interview nearly 25 years ago here on "Nightline." If I may interrupt, there's a little bit of a problem in getting people to talk critically about the church of scientology because they're scared. No. Reporter: But tonight new claims about the secretive world of scientology and the man at its center. Let's face it. Scientologists have not been treated like members of religions ever. Reporter: From an unusual source. You spent 12 years here? 12 years. Reporter: Ron miscavige, David miscavige's father is speaking out for the first time exclusively to ABC news. You have written a whole book about your son, and you've called the book ruthless. It's a pretty damming charge to level against your own child. He wasn't always that way. Reporter: Roin miscavige said he wrote the book because of a policy called disconnection which he says tore his family and many others apart. I raised him and to come to this, what the hell is this? It's nuts. Reporter: The church says Ron's book co-written by a former church member is filled with half truths and outright lies. It's in my view, a literary forgery. Reporter: Scientology granting us a rare interview with attorney for the church. Reporter: What has David miscavige's response been to the book? On a personal level, I think he's very sad his father would do this. There seems to be no explanation exempt his father is trying to make a buck. Reporter: While the church is attacking him, he's getting support from a prominent voice. I'm going to get there first. Reporter: Leah remny, former star of the king of queens who left the church and wrote a book called "Troublemaker". You look like a million bucks. It's great seeing you. How are you? Good. You're getting better looking. Reporter: You haven't seen each other since you were both active scientologists? Right. He has a right to tell his story. I have a right to tell my story and so do thousands of others. Reporter: This unusual family history and family feud is set in motion in 1968 when Ron, the father of four, a salesman and aspiring musician starts dabbling in scientology after learning about it at a business meeting. There are certain Ables in society which should cease and we're taking some responsibility for them. Reporter: He says scientology works wonders for him. When I got into scientology, I felt I found what I was looking for. It had a lot of answers to life. On a basic level. Reporter: So many answers, so many level-changing benefits. Ron feels a duty as a parent to introduce his son David to scientology as well. He hopes somehow auditing, a sort of counselling can help nine-year-old David with his asthma, and after his first session -- About 45 min huts later he walks out smiling, bright. What's happened. He said dad it's handle. So your view was his asthma was cured by scientology? Let's put it this way. It mitigated it considerably. I think it was at that moment he decided he's going to do something like this. Reporter: You think that was the key turning point in his whole life? I know it. Reporter: At age 16 David miscavige joins the see organization, the religious order of the church and develops a close relationship with church founder, L Ron hub bard. In 1986 when hub ard days, David takes control taking chairman of the board. By this time, David's father Ron has also joined. Quickly Ron says he noticed his son's sharp edged new management stage. He's tearing my apart backstage cursing, yelling, screaming at me. Reporter: One night at a church event where Ron is performing he says David gives him an extended tongue lashing with other people looking on. When he's scream agent you do you ever think I changed this guy's diapers? No kidding. Of course I did. And that isn't the only time it happens. Reporter: And he says life for members deteriorates. He describes crushing workloads, restrictive rules, a rigid lifestyle and a lack of sleep. As time went on, it slowly went downhill and got worse and worse. Reporter: The church rejects the claims telling us long and hard hours and a restrictive lifestyle are part of the lifestyle they sign on for. They'll say it couldn't be a better place to work. These people have dedicated their lives to something they believe in. They believe that scientology can really help mankind and the world in general. And they're working very hard at that. Reporter: As for Ron. He was working with first class musicians in one of the best studios in the world. He had nothing to complain about. My name is peter. I'm a song writer. Reporter: The church sent us video testimonials from Ron's former band mates. Ron was an embarrassment to me personally and also letters in which the band mates call him lazy and crude, saying he used racial and ethnic slurs, was a poor musician and a disgusting pig. Reporter: Do you know of any other church that criticizes former members like the church of scientology does? I think it depends on the members. When the Vatican gets attacked, they say something about the attackers. Reporter: If someone leaves the catholic church, do you think they're on this level? Not if they go off and live their life? Reporter: People leave and criticize the catholic church all the time. Exactly, and I think if people in the church are asked for their opinion of this particular person, that you may well get the same kind of R criticism. Reporter: This is the church itself asking videotaping it giving it to us. Well, again, the facts are what they are. Reporter: Ron says the facts are that by 2012 he can no longer bear life in the sea organization. So along with his life who he married after divorcing David's mother. He quits. When Leah remny hears that Ron, the chairman of the board's father has left, she reaches out. I tracked him down. I called him. And I offered my support immediately because I know he must have felt alone when leaving, and I just wanted him to know that we were willing to take them in. That's a big offer. What made you feel motivated to do that? Because there is no -- there really is no place for them to go unless they have family. Which is very rare, outside of the church. Reporter: Ron says quitting the church creates a whole new host of profound problems for him. Coming up, it's father versus son as Ron's departure exposes deep familial riffs erupting into public view. I've never met some of my great grandchildren. I don't know how many there are. That's terrible. That's why I'm doing this. Reporter: Stay with us. Ellen,
This transcript has been automatically generated and may not be 100% accurate.