Los Angeles, California (CNN) In this celebrity mecca, where the issue usually is "Who's your daddy," actor Jason Patric is engaged in a court fight that raises an even thornier question: What is a daddy?

Listen to him talk about 4-year-old Gus for a moment. He speaks with a father's voice, sharing a father's memories:

"He was an inquisitive little boy. From the time before he could speak he was fascinated with things in the sky -- with airplanes, with the ceiling fan, and we would just sit on the porch at night while his mom was still working and he'd point at all the different planes.

"And then when he could say, 'Planes,' he'd say what they were. And then I'd buy him planes. We'd get airplane books. And then I'd take him to the airport park. He had a great laugh, a great sense of humor. He had more concentration than any child I've ever seen."

But Gus' mother, Danielle Schreiber, tells a very different story. She said Patric, a former boyfriend, was little more than "a visitor" who provided genetic material but "had only sporadic contact with Gus during the first two years of his life." Patric never bought a crib and never set up a bedroom in his home until he filed his paternity suit, she said in a statement to CNN. He never so much as changed a diaper.

"There was no co-parenting with Patric, or anything close," she said.

Schreiber, who turned down CNN's request for an interview, maintains through her lawyers that Patric had no interest in being a father when he donated sperm at an in vitro clinic in 2009. She said he insisted she not tell anyone and that his name be kept off the boy's birth certificate, which it was. Now, she said, he is using the courts -- and public opinion -- to interfere with her right to raise Gus as a single mother.

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Because Patric and Schreiber lived together but never married, the court battle over whether he should be a presence in Gus' life illustrates how far the law has fallen behind advances in science and an ever-changing society, said Berkeley Law professor Melissa Murray.

His unmarried status -- not hers -- has led to a painful and protracted court battle, complete with his-and-her morning show appearances, a website, Stand Up for Gus (his), a restraining order (hers), appeals to the California Legislature (his), even a legal attempt (hers) to keep him from publicly speaking or tweeting Gus' name.

Patric said that's discrimination, and it's unfair. But Schreiber's lawyers said it's just as unfair to assume that a single working woman can't decide to have and raise a child on her own.

"Public policy favors a child having more than one parent," said Patric's lawyer, Fred Silberberg, who said he considers keeping his client, a willing father, out of the boy's life to be "a great injustice."

Not surprisingly, her lawyers disagree.

"If people in the public say 'I'm not going to tolerate any family other than the Ozzie and Harriet family,' then they are out of touch with reality and they are out of touch with fairness," said Fred Heather, one of Schreiber's lawyers.

Beyond the gender divide, the court battle further tests our notion of family during evolving times in which men can legally marry men, women can legally marry women, and babies can be conceived in laboratories. Same-sex marriage is now legal in 19 states and the District of Columbia. It's up for discussion in every other state.

"So much of our law is oriented on marriage," said Murray, who is affiliated with the Berkeley law school's Center on Reproductive Rights and Justice. "This is a clarifying case. It's kicking the can to the legislature and saying 'Make the law look more like the way people live.'"

Patric had not seen Gus in 66 weeks when he spoke with CNN on a recent Wednesday afternoon. He talked for more than an hour at an outdoor coffee shop near the sprawling downtown courthouse where this city's broken families come to either fix it or end it. It's where Patric is fighting to win recognition as Gus' legal father.

Patric, 48, drove Schreiber to the Los Angeles clinic where Gus was conceived with his sperm and her egg on March 9, 2009. She signed the paperwork listing them both as the "intended parents." This was for medical consent only, she said; he said it proves he was meant to be the daddy.

Gus was born on December 3. Patric drove mother and son to Gus' circumcision when he was 8 days old. They celebrated Gus' first birthday together, he said. And they celebrated his own birthdays. Gus called him "Dada."

Someone in search of good genes could do far worse than a dark-haired, blue-eyed movie star who once dated Julia Roberts. Patric is perhaps best known for the 1980s vampire classic "The Lost Boys," and his family tree includes other actors. His maternal grandfather was the iconic late comedian Jackie Gleason of "The Honeymooners" fame; his father, Jason Miller, played the role of Father Damien Karras in "The Exorcist." Miller also wrote the Pulitzer-Prize winning play "That Championship Season."

Schreiber, who hails from an accomplished East Coast family of lawyers and business professionals, is a quadruplet. Her mother, Linda, was featured in People magazine in 1978 for what then was a rare feat: giving birth to four babies at once.

Schreiber, 41, grew up in Greenwich, Connecticut, and Westchester County, New York, where she attended public schools and excelled at sports, especially lacrosse. She studied American civilization at Brown University, was involved with Legal Aid and the ACLU and has a Rolfing massage therapy practice in Los Angeles.

She and Patric met through her practice in 2002. Four years later, they started trying to have a family but were unsuccessful. They broke up in 2008, she said, but stayed friends and he was a part of Gus' life until a falling out in June 2012.

How much a part of Gus' life Patric was remains in dispute, like everything else in this case. She said he wasn't around, that there was no crib at his house in Santa Monica, which was not far from hers. He said he had a crib in his apartment in New York, where he was spending most of his time, and that toys were strewn around the place. He said there were visits back and forth, and lots of time on Skype. And he said he has the photographs, videos and cards to prove it.

The romance briefly rekindled when Gus was about a year old, but Patric said he knew things weren't going to work out. He recalls the end:

"Two years ago, my birthday was on Father's Day. I went out with Gus and Danielle. She got me a big Father's Day cake with Gus' picture on it for my birthday. I have pictures of that and the cake. Within 10 days of that, she said, 'I have a lawyer, call a lawyer,' and would not speak to me again."

Jason Patric and his lawyer, Fred Silberberg, appeared on a panel in April at Fertility Planit, a family planning conference held at UCLA.

He wasted no time in filing a paternity claim -- on June 26, 2012 -- citing a California law that states that a man is presumed to be a parent if he welcomes a child into his home and publicly represents the child as his own.

But that law is contradicted by another, which was enacted to protect sperm donors from after-the-fact child support claims. That law states, in no uncertain terms, that a man has no parental rights if he donates sperm through a doctor to anyone but his wife.

Already, this case has grappled its way through mediation, Los Angeles Superior Court, a California appeals court and back again. Halfway through a trial in Los Angeles, the judge, Mark A. Juhas, cited the sperm donor law and dismissed Patric's paternity claim.

"I don't think anyone is going to prevail as a result of this," the judge said. "I think at the end of the day that everyone turns out to be worse off, and certainly I think that Gus turns out to be worse off as a result of where we're going to end up."

Patric appealed, and last month the appeals court sent the case back to the Superior Court for trial, once again giving him the chance to prove he is Gus' father. The appeals court reasoned that it may have strictly applied the sperm donor law in a previous case involving an unmarried couple that tried to have a child together naturally.

"We should look beyond the words of the statute," the court wrote, "to find legislative intent for a public policy favoring a finding of paternity where, as here, the mother was in an intimate relationship with a known donor and also attempted to conceive naturally, albeit unsuccessfully."

Patric's lawyer, Silberberg, said the decision shows the courts are slowly starting to see that the way families are created has changed. "There are multiple paths to becoming a father and the law is now able to recognize that, even in the case of someone who used IVF out of wedlock," he said.

Court cases involving children born out of wedlock unfold under seal, behind closed doors. It is just another quirk in California's outdated family code. But the appeals court's decision was certified for publication, which made some details of Patric's paternity case a matter of public record.

He has been vocal, advocating for fathers' rights and campaigning against what he calls parental alienation with his website. But Schreiber has been more reticent, making just one television appearance -- on "Today" -- and offering just a few written statements.

She has maintained that she always intended to raise Gus on her own, without Patric's help. She said she researched the law and believed when she accepted his sperm that he could not later claim paternity.

"I entered motherhood prepared to undertake all the necessary responsibilities: the emotional, physical, financial, practical and logistical aspects of being the parent," she said in her statement to CNN. "I organized my life around it. Becoming a single mother was not only an informed decision, it was the right decision for me."

Schreiber's lawyers have until June 23 to file an appeal with California's Supreme Court, and they plan to take advantage of every second, said lead litigator Patricia L. Glaser, a veteran of some of L.A.'s most contentious legal battles.

On the day CNN caught up with Patric and enough lawyers to field a softball team, the case went before two judges before a routine hearing date could be set. During the three hours it took to accomplish this task, Patric was referred to as "the father," "the presumptive father" and "the sperm donor."

Glaser used the phrase "as expeditiously as possible" at least four times during proceedings that seemed anything but expeditious. After all, she gains nothing from haste as Gus is living full-time with her client and the court does not allow Patric to contact her or visit the boy.

Both sides now have spin-doctors to advise them, and to handle the media. Besides Glaser, team Schreiber has added master public relations crisis manager Michael Sitrick to the payroll.

As it heads toward trial, the case is taking on some of the more unsavory he-said/she-said aspects of family court, where drama runs high and breakups can leave a lingering, bitter aftertaste.

Patric was asked whether he was prepared for the ugliness of a custody fight. He said that he was willing to do whatever it takes to see Gus again, pointing out that he has spent 30 years in the public eye without so much as a scuffle with the paparazzi. He challenged CNN to conduct a Google search and, indeed, he appeared to have been a relatively low-profile celebrity until the paternity case.

There was one arrest -- in Austin, Texas, in 2004; the charges of public intoxication and resisting arrest were later dismissed, court records show. Patric sued the city of Austin and the arresting officer in federal court, alleging false arrest and excessive force, but lost the case.

Even as Patric spoke with CNN, the gossip site TMZ was preparing a story based on allegations that he struck his "baby mama" with a telephone and called her ugly, anti-Semitic names. He and his lawyer already knew it was coming and were busy working on their denial in the corridors during breaks in the court hearings.

"If I did what they claim I did," he said, "if I'm a member of al Qaeda, if I killed JFK, if I'm a racist or an anti-Semite or had illegal immigrants work for me, then why did (Schreiber) have a child with that man?"

When he talked about the issues at stake, Patric was passionate and articulate. If he felt any anger, he held it in check during the interview. He did not badmouth Gus' mother.

In Patric's version of the story, he is a loving father whose son was maliciously snatched away from him by a woman scorned. He said he's being discriminated against by the system.

But she and her handlers say he abused her -- verbally, physically and emotionally -- and is continuing to do so with a legal fight that has thrust her and a 4-year-old boy into the limelight against their will.

Schreiber and her representatives say Patric was verbally abusive in front of Gus, and that is why she won't allow him to see the boy. She obtained a restraining order against him in November, and he has been barred from contacting her for a year. She testified in open court and also detailed her allegations in court declarations.

But Patric testified that the allegations are not true. "Jason denies any kind of abuse. Unequivocally," said Silberberg.

Although Schreiber also purchased sperm from an anonymous donor, Patric has no doubt that he is the boy's biological father. Nobody really denies it, not Gus' mother or her army of lawyers, and they continue to refer to him dismissively as "the sperm donor."

The label rankles Patric. As a mere sperm donor, he might as well be a stranger to Gus. But the words he chooses don't sound those of a stranger.

"I taught him not to be afraid of bees; they're just pollinating. How to walk barefoot: the grass is spongy, the cement is scratchy, stop at the corner. Toilet training, guitar, music, how to express yourself ... I taught him about Elvis from an early age. I said, 'You're compassionate. Do you know what that means, Gus? It means you really care about other people.' And then he went, 'Beep, beep, beep, like Elvis.'"

Sunday will mark the second Father's Day that Patric has spent without Gus.

"Of course it's incredibly sad," he said. "It's the most important thing you can be to someone, a parent, and that's what I've done. It's about the boy, and you have to make everything about him."

He is confident he will someday win in court.

And if he doesn't?

He will take comfort in knowing that Gus, who will be 5 in December, "will have a record of how hard I fought for him."