Shrek, star of four hit animated movies, has been called quite a few things since he first appeared on the big screen in 2001. "Green", obviously; "loveable", certainly; "ugly", cruelly. But Jewish?

Well, yes. Hollywood screenwriter David Weiss has revealed that, while working on the movie Shrek 2, he turned for inspiration to the words of his rabbi and in the process koshered the ogre.

"We were trying to figure out the theme for the film that marriage is hard," he says, speaking from Los Angeles. "But people don't need to pay $12 for a movie theatre ticket to hear that. So I told the director a story that I heard from my rabbi about what love means. Love means what's important to you, is important to me. This is incredibly hard for a man, because it means whatever your wife is talking about, even if it is trivial, it's important to her, and if you love her, it's important to you.

"We didn't say lets make that the theme, but if you look at Shrek 2, I feel that it informs everything Shrek does."

Weiss is no stranger to conversions, having had two himself. Raised as a Reform Jew in California, he became a Christian when he was 18 before reverting to Judaism again later in life, this time as an Orthodox Jew.

We were trying to figure out the film's theme. I remembered what my rabbi had said about love

"The Reform movement I was growing up in wasn't particularly optimistic, there was a sense of a siege mentality, that Judaism was at risk of people leaving and they desperately needed us to all stay Jewish," he recalls.

"I was an insecure kid and I was looking for assurances about the meaning of life, why we are here. There was a real focus on the Holocaust at the time I was growing up - it was very disconcerting, and my religion didn't offer me peace of mind. So I was looking for something that told me that life has a purpose.

"I lived in a beach town, in Ventura, and most of the kids in school were Christian. When I first came into contact with them I was very antagonistic and challenged them on their theology, but as time went on and I started to go to church with them. They were so warm and inclusive - I liked it. There was talk of heaven and eternity and that God loves you. I wanted out of Judaism and wandered into Christianity."

So Weiss converted to Presbyterianism. His family were not pleased.

"My mum was very upset but she tried to keep a dialogue going. My dad kept quiet about it - he didn't want to hear about Christianity and that put some distance between us. My grandmothers were heartbroken.

"My mother unfortunately passed away before she could see me come back to Judaism - I was 19 when she died. People said it was my fault because I had converted. Luckily her mother lived to see me come back - she is 105 now."

It was while Weiss was working on his first film, All Dogs Go To Heaven, in 1989, that he rediscovered Judaism. "I met a young animator called David Steinberg. He was the first Orthodox Jew I had ever talked to, and lo and behold he was not as fanatical and terrifying as I had been led to believe by my fellow Christians.

"When I got back to the States, I continued to be intrigued by what I heard from him about Judaism. I was stunned to find out how much the Church had got wrong about our teachings and I was even more stunned to find out that what I liked about the Church was our teachings. It seemed insane to go Orthodox but at the same time I couldn't find Christianity as fulfilling anymore - there was a torment for a few years.

"When I eventually met my wife she enrolled us in an introduction to Judaism class and she loved it. We became Orthodox when she wanted to dig deeper and have a conversion that no one could question. We did that process and remarried in an Orthodox synagogue."

Weiss's credits include several movies and television shows, but he is known is his industry not just for his screenwriting work. He was one of the leaders of the writers' strike that shut down much of Hollywood's output during 2007 and 2008.

As vice president of the Writers Guild of America West, he helped organise the effort to force a better pay deal from the major studios, which saw stars like Ben Stiller and Julianne Moore join writers on the picket lines.

"We were forced to go on strike, we certainly didn't want to," Weiss recalls. "As a board member I was on the picket line. There are pictures of me marching around in circles, people with a bull horn and carrying signs."

"I would do the early morning run, head out at 6am and go from studio to studio to shore up the troops and give them encouragement.

"I was also a peacemaker between the more powerful writers who were anxious to get back to work and those who felt it was important to fight."

Although the strike was called off over two years ago, the final outcome of the dispute is still not clear - talks between the studios and the Guild are ongoing.

"We are about to go into more negotiations and I'm not allowed to say any more," says Weiss. "But both sides are very eager to avoid conflict again so I'm hopeful that negotiations will be fruitful."

Weiss's latest project in another animated movie, again starring a hero in a primary colour. The Smurfs , featuring the bright blue children's characters, is due to be released later this year.

Will they be Jewish too? All Weiss is saying is: "I will draw on things that have a Jewish tinge to them. So much of our religion exports nicely."