Tom Cruise is the victim of religious prejudice and should not be attacked for being a Scientologist, his film-making partner has said.
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Paula Wagner, who co-owns the United Artists studio with Cruise and is not a Scientologist, said his religion had "no bearing" on his professional life.
The actor recently came in for ridicule after a video of him talking about his beliefs surfaced on the internet.
Wagner said the "vitriol" that had been aimed at Cruise was "discouraging".
"I am not a Scientologist, nor are most of the people Tom and I work with, but that doesn't mean I can sit by silently while he is attacked for his religious beliefs," she said.
"As a film-maker and an American, I feel strongly that an individual's religion should have no bearing on their professional life.
"I have always believed that Americans celebrated these differences."
Paula Wagner took over United Artists with Cruise in 2006
Wagner has served as producer or executive producer on many of Cruise's films, including Mission Impossible, Vanilla Sky and War of the Worlds.
"It's easy to mock an out-of-context video," she continued. "But that doesn't change the fact that Tom Cruise is one of the hardest-working and nicest human beings I have ever known."
In the four-year-old video, Cruise discussed how he wanted to spread the message of Scientology and said a Scientologist driving past an accident was "the only one who can really help".
He also said: "We are the authorities on getting people off drugs, we are the authorities on the mind, we are the authorities on improving conditions... we can rehabilitate criminals... we can bring peace and unite communities."
He said Scientologists had no time for "spectatorism" but instead had "a responsibility to educate and create the new reality".
"You are either in or you're out," he said.
A Scientology spokeswoman said the full video could be seen in its churches.
What appeared on the internet was a "pirated and edited" version of an acceptance speech Cruise had made in 2004 after receiving a "freedom medal" from the International Association of Scientologists, she said.
A new biography of the Hollywood star has also come under fire from those close to Cruise.
Wagner said Tom Cruise: An Unauthorised Biography by British author Andrew Morton was "filled with distortions and outright lies that no sensible person will take seriously".
And Cruise's lawyer Bert Fields branded it "sick stuff" that was full of "tired old lies".
They included the "nutty" claim that Cruise was second-in-command at the Church of Scientology, he added.
The book's publisher has said it stands by the book and the author.