Georgia's doubting dads can thank Carnell Smith for being able to challenge the paternity of a child they suspect is not their own.

He successfully lobbied the state Legislature in 2001 to change the law so men can challenge paternity at any time -- a move made easier now that DNA testing is readily available.

The new law took effect in 2002. And a year later Smith became the first person to use it to overturn a paternity ruling that required him to pay child support even though DNA evidence proved he was not the father.

Family law attorney Randy Kessler, who represented Smith during part of his child support case, called him a "gold-star client."

"He did his own research and legwork," Kessler recalled. "It was like having another lawyer in our corner."

Smith prefers to think of himself as a "rebel with a cause."

But he never guessed during the 11 years he helped raise his purported daughter that he was being duped.

An ex-girlfriend gave birth to the girl on Dec. 29, 1988, after a 2 1/2-year relationship with Smith ended. But Smith fully embraced his role as a parent, even when he married two years later and had another child.

It wasn't until he and the ex-girlfriend got into a dispute over his child support payments in 2000 that a friend urged him to take a paternity test.

"I had no suspicions," Smith said. "I figured I had nothing to lose, but I fully expected to prove to him that she was my biological daughter."

To Smith's amazement, the test proved otherwise.

Previously under the Georgia code, a man's conduct toward a child was considered evidence of fatherhood regardless of whether there was a biological link between them. Many other states had similar laws.

So entrenched was this belief that DeKalb County Superior Court Judge Edward Wheeler ordered Smith to continue paying child support for his ex-girlfriend's daughter, even after the DNA test showed he wasn't the father.

Smith enlisted the help of a neighbor, state Rep. Stanley Watson (D-Decatur), in getting Georgia's law rewritten in 2002.

And after getting the ruling in his case overturned in 2003, he went on a mission to reshape public policy about establishing paternity nationwide.

In the years since, Smith has helped get paternity fraud laws passed in several other states, including Wyoming, Florida, Oregon and Delaware.

He's passionate about the cause because he believes it's not just doubting dads who are harmed by being kept in the dark. Many children are also confused and hurt, he said, and true biological fathers are robbed of the opportunity to be a parent.

Smith said finding out he wasn't the father of his ex-girlfriend's daughter was like having a child die. His ex-girlfriend cut off his contact with her daughter after he challenged paternity. He has not seen the child since.

But Smith said he has no regrets about taking the DNA test. He said the truth freed him from the court's control.

Now 50 and living in Decatur, Smith continues to operate his nonprofit organization, US Citizens Against Paternity Fraud. He has appeared on numerous television and radio talk shows, and he is producing a documentary about his experiences called "Hostage of the State."

Along with his wife of 20 years, Lisa, Smith runs 4Truth Identity, a Decatur business that provides DNA testing services for maternity, paternity and immigration cases. Lisa Smith answers the phone, sets up appointments and handles administrative duties while her husband is the mouthpiece of the company.

"He's the crusader; I'm there to be kind of the cheerleader," she said with a laugh.

The couple has a 12-year-old daughter. Smith also became a grandfather last year by an adult son from a previous relationship.

Meanwhile, the other daughter he once counted as his is now a college student. The Smiths said they spoke to her on the phone about a year ago and made plans to meet her for lunch, but she canceled at the last minute.

"I gave her the open door whenever she's ready to meet and talk," Smith said. "I would love to have a relationship with her."