Earl E. Devaney, who began his career as a Secret Service agent guarding President Richard M. Nixon and rose to become one of the American government’s most aggressive and feared internal watchdogs, died on April 15 in Boca Raton, Fla. He was 74.

His son Michael said the death, at a hospital, was caused by complications of a heart attack.

Friends and foes alike called Mr. Devaney the Big Man, and not only because he long retained the imposing heft he once yielded as a college football player.

An administrative entrepreneur, he helped build the financial-fraud arm of the Secret Service, gave real teeth to the enforcement capabilities of the Environmental Protection Agency, took down a corrupt agency within the Interior Department as its inspector general, and managed to keep the vast 2009 economic stimulus effort virtually fraud free.

Mr. Devaney had a flair for flashy cases and headline-grabbing congressional testimony, not, by his account, for their own sake or to boost his career, but for their deterrent effect.

“You can have an inspector general who lurks in the shadows,” Felicia Marcus, a fellow at Stanford University who worked with Mr. Devaney at the E.P.A., said in an interview. “He did not lurk in the shadows.”

In his office at the Interior Department he kept an alligator head with a camera hidden inside, which he had used to film a department official engage in a bribery deal while on a fishing trip in the Louisiana bayou.

“When an assistant secretary comes in and asks about it, I tell that story and they get a little unnerved,” he told The New York Times in 2009.

When he arrived at the Interior Department in 1999, many people in the leadership had never met his predecessors, nor did they need to — the typical inspector general quietly issued reports and might testify before Congress once in his or her career, but rarely did someone in that role make an active effort to squash wrongdoing or to bring transparency to government operations, two things Mr. Devaney relished doing.

“Ed was a standout because he recognized the full breadth of the responsibilities of an inspector general,” Danielle Brian, executive director of the nonpartisan Project on Government Oversight, said in an interview.

His biggest case emerged during the George W. Bush administration, in 2008, when he released a series of reports showing widespread misconduct at the Minerals Management Service, a branch of the Interior Department that collected about $10 billion in royalties on mining on federal property.

The opportunities for corruption were immense, and Mr. Devaney and his team showed that government officials in the service had manipulated contracts and received sports tickets and other gifts from industry officials while engaging in drug use and sex with oil-company employees in what he termed “a culture of ethical failure.”

Though the department tried to reform the service, the failures identified by Mr. Devaney were too great, and it closed in 2011.

In another investigation, he fingered J. Steven Griles, the deputy secretary of the interior, for corrupt practices related to Jack Abramoff, the disgraced lobbyist; Mr. Griles denied the accusations but was later convicted of lying to Congress about his ties to Mr. Abramoff and sentenced to jail.

Mr. Devaney’s most high-profile post was his last. Though he had promised his wife, Judy, that he would retire so they could move to Florida, Vice President Joseph R. Biden in 2009 asked him to act as the internal watchdog for President Barack Obama’s gargantuan economic recovery effort.

“I practiced all weekend saying no” to Mr. Biden, he told The Washington Post in 2011. “Something like ‘I’m really honored’ or ‘Let me give you some names you could consider instead of me.’”

But then Mr. Biden took him into the Oval Office, where President Obama did the asking.

“I hadn’t practiced saying no to a president,” he said.

Though he stayed in the job only a few years, he was once again transformative. As the head of the Recovery Accountability and Transparency Board — he preferred its acronym, the R.A.T. Board — he oversaw the implementation of Recovery.gov, where members of the public could track the progress (or lack thereof) of government programs in their area, and he encouraged people within and outside the government to report abuse where they saw it.

“I want to make it possible for Mr. and Mrs. Smith in Ohio to see exactly how the money is spent,” he told The Times.

His efforts paid off: There had been virtually no evidence of fraud when he retired on Dec. 31, 2011, to much acclaim from members of both political parties.

Earl Edward Devaney was born on June 8, 1947, to John and Claire Devaney in Reading, Mass., a northern suburb of Boston. His father owned a series of small businesses. His mother was a model and actress.

He attended Franklin and Marshall College in Lancaster, Pa., where he studied government, played on the football team as a lineman and graduated in 1970. Early on, he felt the draw of a career in criminal justice and worked summers as a police officer on Cape Cod.

Along with his son, he is survived by his wife; another son, Matthew; and five grandchildren.

From college Mr. Devaney went directly into the Secret Service, where he worked on the presidential details for both Nixon and Gerald R. Ford. It could be perilous work: At one point he came under fire from a deranged woman who thought he was President Ford.

He later transferred to the agency’s newly created white-collar crime division, where he distinguished himself as a particularly effective cop working the beat within complex operations like the banking system.

Mr. Devaney left the Secret Service in 1991 to work at the E.P.A., where he strengthened the agency’s historically weak enforcement efforts.

And while he had long since traded his Secret Service agent’s gun for a desktop computer, he could still move decisively when necessary.

Once in San Francisco, he was walking with three E.P.A. colleagues, including Ms. Marcus, up a hill after dinner. Mr. Devaney was walking behind her.

“I felt a brush of wind against my neck, but didn’t think much about it,” she recalled. “Then I turned around and saw that someone had tried to grab something out of my purse — and that just as quickly, Ed had grabbed the man and pushed him against a wall.”

“He had this mix of grace of strength that is remarkable,” she said.