Thomas is no relation, biologically, to the child who calls him "Father." He was never married to the boy's mother. What's more, the mother doesn't want him to have anything to do with her son.
Yet late last week, in a decision that could take on national significance, California's Supreme Court ruled that Thomas is indeed the boy's legal father, and that he will retain custody against the mother's wishes.
To many, the ruling is being seen as one of the strongest legal statements yet that fatherhood is determined more by behavior than biology. It has also been called a victory for children here, who can now be placed with the most suitable parental figure even if there are no blood or marital ties.
But, more broadly, the decision is simply the latest example of how the notion of "family" in America is changing both in the courts and at kitchen tables.
With the breakdown of the two-parent family and the development of new reproductive technologies, an increasingly complicated web of stepparents and egg donors, half-brothers and surrogate mothers has made traditional family roles and responsibilities more murky.
Countrywide, the effort to define these relationships legally is just beginning, and California's step might serve as a signpost for states seeking clarity.
"You're seeing [cases like these] coming out more and more because of the challenges to the nuclear family," says Nanette Elster, a family-law expert at the University of Louisville in Kentucky. "We don't have such a clear definition of what family is anymore. This is a different take."
During the past decade, a raft of lawsuits has underscored the changing nature of families.
Earlier this year, an infertile Utah couple that used a surrogate mother to have a baby sued the state because of a law that decrees that the birth mother is the legal mother. To become the legal parents, the couple has to adopt the child.
In another case of a type that has become common, a Texas man recently sued to stop child-support payments after he learned the child he had thought was his for 13 years actually was not. He lost the case.
The California ruling, while different, strikes a shared theme with these others: "It points to the idea that biology and genetics might not be the best standards [for parenthood]," says Ms. Elster. "It's one way of saying that you have to look at other factors and see what's in the child's best interests."
According to the state Supreme Court opinion, the child's welfare was the overriding factor in its decision. Thomas had met the child's mother when she was already three months pregnant. They moved in together a few months before the birth in 1995, and Thomas's name was on the birth certificate. After an on-again, off-again relationship that included incidents of abuse on both sides, the two split permanently four years later.
With the biological father nowhere to be found and the mother struggling with drug abuse, Thomas took custody of the boy, Nicholas, and sought to become his permanent and legal provider.
In approving the request, the court noted, "Thomas has lived with Nicholas for long periods of time, he has provided Nicholas with significant financial support over the years, and he has consistently referred to and treated Nicholas as his son," while the mother has been "a frail reed for Nicholas to lean upon." (Because the case involves a child, none of the last names have been released.)
Those are important words, experts say. Courts have often claimed to be looking out for children's welfare, but California's decision that responsibility is a more important measuring stick than biology is beyond what any other courts have ruled.
"Courts have struggled when a child's needs go past the traditional view that there is a biological mother, and a biological father, and those are the parents," says Bruce Clemens of the Beverly Hills, Calif., law firm Jaffe and Clemens. "[But] they're finding that an existing father is better than no father."
In some ways, courts and society have acknowledged this for decades, even centuries. Husbands who have had unfaithful wives or wives with children from other marriages have long been seen as legitimate fathers, though they have no biological connection.
What California has done, though, expands that field of accepted fathers to include even those who never married the child's mother.
"[It] is very important as a way of achieving more genuinely equal treatment for all children, regardless of the marital status of their parents," says Joan Hollinger, a law professor at the University of California in Berkeley. "A man like Nicholas's father doesn't have to adopt Nicholas. He basically grows into his position by his behavior."
For that reason, most experts don't foresee a rash of lawsuits to take kids away from parents. Thomas was able to win custody only because he had been a prominent figure in Nicholas's life for a long time and had identified himself as the father.
"The father legally is the one who has been taking the kid to soccer practices," says Janet Sherwood, a lawyer in Corte Madera, Calif. "He has to have been participating in the child's life for a long time with the mother's knowledge and consent to be able to do this."