Justice of the Peace Guy Herman was sitting in his office one day when a prosecutor walked in to file charges for improper campaign-finance reporting. Against himself.

The man was Ronnie Earle, the Travis County district attorney, bringing a self-incriminating complaint for tardy reporting in 1981 and 1982.

"He had missed the deadline by a day," says Mr. Herman, now a Travis County probate judge. "He could have filed that report late and nobody would have paid any attention. But instead he came in and said, 'I violated the law and should be fined.' So I fined him."

$212 to be exact.

Herman says it offered his first glimpse into how seriously Mr. Earle takes the integrity of the political system. It would not be his last.

Because the Texas Attorney General's office does not have the authority to prosecute those suspected of committing crimes in their dealings with the state, the responsibility falls on Earle and his band of prosecutors in Travis County, home of the state capital.

It is a responsibility he has embraced, prosecuting 15 high-profile cases against Republican and Democratic politicians during his 27 years in office. Many have drawn sharp criticism from both parties.

Yet no case has been more important, or controversial, than the one Earle is now pursuing against a political action committee tied to House majority leader Tom DeLay (R) - one of the nation's most powerful politicians.

To Earle partisans, it's an example of his fearlessness in pursuing political malfeasance, a trait they say makes him the state's, and perhaps the country's, top ethics cop. But detractors see the investigation as a witch hunt, another case of the silver-thatched prosecutor acting out of political motivation and for personal gain.

Mr. DeLay calls the Democratic Earle "vindictive and partisan." So far, three of DeLay's associates have been indicted on charges of illegally funneling hundreds of thousands of corporate dollars to state GOP candidates in 2002. The Republican sweep that year fueled redistricting efforts in Texas that deepened Congressional control in 2004.

Preparing for the possibility that DeLay might be charged, Republicans in Congress recently voted to change their rule requiring an indicted leader to relinquish his post.

For his part, Earle says the attacks are no different from those by the 15 other politicians he's prosecuted in almost three decades as Travis County DA. All have accused him of being politically motivated. "What else are they going to say?" he asks.

A fourth grand jury is convening in Austin, in the case Earle calls the most important of his career. "I take very seriously the prohibition against corporate and labor union money polluting the electoral process. It is a hallowed inheritance from our Texas forbearers and is central to the protection of democracy."

Indeed, to those who know him, Earle has always exhibited a strong moral streak - from his formative years growing up in a small town outside Fort Worth, to his time on the Austin night court, to his political service in the state legislature. But they contend his morality is tempered by his compassion.

"Ronnie is very principled and will do the right thing even if it isn't the smartest political thing to do," says Ellen Halbert, a victim's rights advocate who first met Earle when he was prosecuting the man who raped, beat, and stabbed her in 1986. "But he is also very sensitive. He can get emotional about a sunrise or a sunset - and I have seen him do that."

Earle was born and raised on a cattle ranch in Birdville, Texas, where pronouncing all the town's consonants got you beaten up. He was an Eagle Scout, earned money life-guarding, played football, and was president of the student council.

"Ronnie is the beneficiary of a well-grounded childhood in small-town Texas, and he came up in a more innocent time, both culturally and politically," says Ken Oden, a former Travis County Attorney now in private practice. "And I think his early years have made him a better prosecutor."

Earle enrolled at the University of Texas at Austin in 1960 with an eye on journalism, but struggled with typing because his fingers had been twisted in a football injury. His professors told him C's in journalism were not good enough, so he went to law school.

After graduating, he worked in Gov. John Connally's office before becoming an Austin municipal court judge. Drunks, prostitutes, and petty criminals were the usual night-court fare, and Earle says he learned a lot from both police officers and those they arrested. "It imprinted on my soul the fact that the courts are for the people," he says in an amiable Texas drawl.

Indeed, many describe Earle as a populist. "He really believes that the people govern," says David Anderson, a UT law professor and longtime acquaintance. "He's suspicious of corporate power in all its forms. I don't think he's irrational about it, but ... he's vigilant and zealous about maintaining the individual's power in the political system."

After a brief stint with the Texas Judicial Council, Earle won a seat in the House of Representatives in a 1973 special election. He served 3-1/2 years before District Attorney Bob Smith retired and Earle threw his name in.

Many were surprised, says Bill Allison, a lawyer who sometimes hitched a ride to work with Earle when he was a municipal-court judge. "Ronnie was not a trial lawyer. But he campaigned on the promise that he was going to leave the lawyers alone and run the office, and Austin was ready for that change."

Unlike most states, Texas does not give its attorney general the power to prosecute criminal acts at the state level. That task goes to the Travis County district attorney - a responsibility Earle took on, forming a public-integrity unit to look into such abuses.

Over the years, there have been bills to defund the controversial unit and to transfer its power to the attorney general's office. But the unit has persisted and Earle has prosecuted 12 Democrats and three Republicans - most of them successfully.

There have been some notable missteps, though, the biggest in 1994 when he went after GOP Sen. Kay Bailey Hutchison for allegedly misusing state telephones for political business. At a pretrial hearing, the judge questioned the admissibility of the prosecution's evidence and Earle declined to present a case. That led to Senator Hutchison's acquittal, and many saw the DA as an amateur.

"He should have gone ahead and tried the case," says Mr. Allison. "Instead, he dumped it in the grease. And it didn't have anything to do with politics; it had to do with his inexperience." The case still perturbs many in the GOP.

Democrats, for their part, are still upset over the prosecution of Attorney General Jim Mattox for bribery in 1985. While pushing a state lawsuit against Mobil Oil Co., the Democratic AG argued with Mobil's lawyers, which led to his indictment.

He was acquitted and years later, Jim Marston, a civil lawyer in Austin and friend of Mr. Mattox, asked Earle why he went ahead with the questionable case.

"I said, 'Ronnie, how can it be an abuse of power to threaten a lawyer? We threaten each other all the time.' He told me that elected officials are held to a higher standard. They are supposed to be [above suspicion] like Caesar's wife." It was then that Mr. Marston realized how deep Earle's principles run. "Ronnie Earle is a Boy Scout who is offended by wrongdoings, chief among them, public officials' abuse of power."

References to classic literature are common with Earle, a self-described voracious reader who favors philosophy, religion, and psychology in his spare time. He and his wife, Twila, have been recognized for efforts to strengthen family and build community.

"For Ronnie, it's not just 'Can we put someone in jail?' It's 'Can we prevent crime?' " says Mr. Oden. "That might make him a limp-wristed sissy-boy prosecutor to some. But make no mistake about it, those who rape, rob, and murder get no safe passage in his county."

While Travis County has the fewest inmates per capita on Texas' death row, few accuse Earle of being soft on crime.

He was roundly criticized for his 1996 prosecution of 11-year-old Lacresha Murray, who became the youngest person in Texas to be charged with capital murder. The girl was twice convicted of beating a 2-year-old in her care, but both decisions were overturned.

Deliberate in the capital cases he sends to juries, Earle is well known for examining an issue from all angles before acting.

"If I have any complaint about Ronnie, it's that he is overly cautious about who he prosecutes," says Marston. "The fact that it has taken two years to investigate Tom DeLay is a sign not of partisanship, but of being completely careful."

But don't be fooled, adds Allison: Earle is "a politician and if a politician is not watching his or her backside, they are not going to be around for long." Still, he says with respect to a possible indictment of DeLay, "Ronnie is not going to prosecute a lousy case."