Mr. Wright leaves the Capitol building in 1989. (Harry Naltchayan)

Jim Wright, a hard-driving 18-term Texas Democrat who, as speaker of the U.S. House of Representatives, expanded the influence of the office into foreign affairs before resigning from the House in 1989 amid an ethics investigation into his business dealings, died May 6 at a nursing home in Fort Worth. He was 92.

The death was confirmed by Thompson’s Harveson & Cole funeral home in Fort Worth. The cause was not immediately available.

Mr. Wright was a seemingly indomitable figure in the House, where he had risen from obscure Fort Worth congressman in the 1950s to majority leader under Speaker Thomas P. “Tip” O’Neill (D-Mass.) in the 1970s.

In a House career spanning 34 years, Mr. Wright thrust himself most forcefully into the limelight when he succeeded O’Neill as speaker in 1987. Fiery and intense, Mr. Wright could not have been more different from the affable, backslapping O’Neill.

Mr. Wright envisioned a muscular speakership that influenced and generated foreign policy, historically the sphere of the White House and the Senate.

He antagonized the Reagan administration in the 1980s over its Central American policy, particularly aid to the Nicaraguan contras during a protracted civil war. Mr. Wright had a crucial role in brokering a deal that led to peace and democratic elections in Nicaragua.

Poised to become one of the most influential speakers in decades, Mr. Wright endured a year-long investigation by the House Ethics Committee that eroded his power and led to charges that focused on financial gain in violation of congressional rules.

He was the fourth speaker to resign the office, but the first to step down amid allegations of ethical impropriety. His downfall was a pivotal moment in the rise of Rep. Newt Gingrich (R-Ga.), who led the fight for the ethics investigation, and in the House’s transformation from a proudly collegial institution to one mired in partisan rancor.

Although Mr. Wright denied the allegations and was never charged with a crime, he resigned in 1989, saying he acted to protect the House from the “mindless cannibalism” and the vitriolic partisanship fostered by the investigation.

Mr. Wright was not someone likely to generate widespread sympathy during an ethics probe. He had a reputation as a hot-tempered micromanager, and he once nearly came to fisticuffs with a California congressman over a procedural matter.

But he endeared himself to fellow Democrats by stumping for them in their districts and raising money for their campaigns. He also held one of the most popular functions on the Hill, an annual barbecue for which he dressed as a cowboy and played the harmonica.

Although his approach to public speaking tended toward the stentorian, he relished folksy aphorisms and jokes. He memorably described the rhinoceros as one of God’s mistakes: “Here is an animal with a hide two feet thick and no apparent interest in politics. What a waste.”

Mr. Wright’s sharp mind and sharp elbows helped clear his path to power.

“His goal was to make the speakership equal to the presidency,” said historian John M. Barry, whose 1989 book “The Ambition and the Power” focused on Mr. Wright. “He was certainly on the way to doing that.”

Although he often pitted himself against the Reagan administration on legislative matters, no issue brought Mr. Wright as much attention as the fight over aid to the Nicaraguan contras. It became one of the most divisive public debates in Washington.

The Reagan administration had placed the anti-communist contra rebels in Nicaragua at the center of its Central American foreign policy, describing them as “freedom fighters” against Nicaragua’s leftist Sandinista government. But many Democrats, including Mr. Wright, considered the contras no better than terrorists.

In the mid-1980s, the White House found itself immersed in a scandal involving illegal arms sales to Iran, coupled with illegal aid to the contras. Some U.S. officials had allegedly sold weapons to Iran to win the release of U.S. hostages in the Middle East, then diverted the profits from those sales to support the contras, despite congressional prohibitions against military aid.

In July 1987, a White House aide approached Mr. Wright about joining Reagan to broker a peace deal in Central America. Mr. Wright agreed, though many Democrats sensed it was a trap.

According to Barry’s book, the White House enlisted Mr. Wright’s support for a proposal it expected Nicaragua to reject, thinking it could then point to the failure of diplomacy to bolster its case for funding the contras.

The feud with the White House worsened when Mr. Wright began to hold cease-fire talks in Washington with Nicaraguan President Daniel Ortega and Cardinal Miguel Obando y Bravo, the archbishop of Managua, who was seen as a possible intermediary in the dispute.

The White House refused to meet with Ortega during that visit, insisting that he negotiate with the contras before any U.S. intervention. Mr. Wright scolded the Reagan administration for being “literally terrorized that peace might break out,” adding that many Central American leaders preferred negotiating through him because they have “the unfortunate impression that the administration treats them as inferiors.”

After Central American leaders drafted their own peace agreement, Mr. Wright offered his unequivocal support. The accord helped end Nicaragua’s long civil war and led to democratic elections in 1990.

“He was absolutely critical,” said William LeoGrande, an expert on Latin American politics at American University. “The Central American leaders looked to Wright for mediation, for advice and for support. . . . They felt he was committed to make it work.”

Long a target of Republicans, Mr. Wright began his political fall from grace in 1988, after the public-interest lobby Common Cause urged a House ethics probe into sales of the speaker’s book of speeches and essays.

Mr. Wright was suspected of circumventing House rules on outside income by accumulating about $54,000 in royalties from bulk sales of his 1984 book “Reflections of a Public Man.”

The accusation was that in lieu of campaign contributions or speaking fees, which were tightly regulated, groups with business before the House made bulk purchases of the book. House rules exempt copyright royalties.

Based on the information from Common Cause, Gingrich filed a complaint with the ethics panel with the backing of other House Republicans. Mr. Wright and Gingrich had traded insults in the past, and the Georgia congressman was initially perceived as leading a one-man crusade against the speaker.

In April 1989, the ethics committee reported that it found “reason to believe” that Mr. Wright had violated the rules of congressional conduct 69 times. In addition to the allegations about book royalties, he was accused of taking $145,000 in gifts from a Fort Worth developer.

Mr. Wright resigned on June 1, 1989, and his chief deputy, Thomas S. Foley (D-Wash.), assumed the speakership.

Gingrich went on to become speaker after the Republican takeover of the House in the 1994 midterm elections. But ethics charges would tarnish the end of his tenure in Congress, as they had Mr. Wright’s, and he resigned in 1999. When Gingrich, as speaker, faced criticism from the ethics committee over a $4.5 million book advance, Mr. Wright tweaked his former antagonist. By comparison, Mr. Wright said, his own book royalties were “small potatoes.”

James Claude Wright Jr. was born on Dec. 22, 1922, in Weatherford, Tex. His father was a salesman, and the family moved frequently.

Mr. Wright was a Golden Gloves boxer in his youth. During World War II, he was a B-24 bombardier and flew 30 bombing missions over Japan. He recounted his war service in his 2005 book, “The Flying Circus: Pacific War — 1943 — as Seen Through a Bombsight.”

After the war, Mr. Wright won election to the Texas state legislature. He supported an anti-lynching bill, abolition of the poll tax and the admission of black students to the University of Texas law school.

His progressive views, far to the left of many of his constituents, cost him reelection, but he won two terms as mayor of Weatherford before winning a House seat in 1954. During one confrontation on the campaign trail, Mr. Wright knocked down a heckler who called him a communist.

In the House, Mr. Wright was assigned to the Public Works Committee, where he wielded influence over interstate highway construction. He fought for a variety of development programs that benefited his state and became a reliable proponent of the Texas oil and gas industries. He also supported U.S. involvement in the Vietnam War; political analysts noted that his district was a hub of defense contractors.

On civil rights, Mr. Wright amassed a complicated legacy. He voted against the hallmark 1964 Civil Rights Act, saying that a yes vote that year would have ended his political career. He later apologized for his vote, and he supported key civil rights legislation in 1965 and 1966.

Mr. Wright twice ran unsuccessfully for the U.S. Senate in the 1960s, including a bid for the seat Lyndon B. Johnson vacated after Johnson became vice president. In the House, he advanced into leadership positions.

When O’Neill became speaker in 1976, vacating the majority leader’s office, Mr. Wright vied with three other contenders for the job. Seeing an opening as a moderate whose state had one of the largest Democratic delegations. Mr. Wright positioned himself as everybody’s second choice and won by a single vote.

After leaving Congress, Mr. Wright took to the speaking circuit, wrote a column for the Fort Worth Star-Telegram and taught government at Texas Christian University. In the late 1990s, he became ill with tongue cancer, which slurred the old orator’s speech. He had to relearn diction.

His first marriage, to Mary Ethelyn Lemons, ended in divorce. Their son, Parker Stephen Wright, who had Down syndrome, died in 1958.

In 1972, Mr. Wright married Betty Hay, a former staff member for the House Public Works Committee. Besides his wife, survivors include four children from his first marriage.

“I think I was probably obsessed with the notion that I have a limited period of time in which to make my mark upon the future,” Mr. Wright told The Washington Post in 1989, after he resigned from the House, “and, therefore, I must hurry.

“Maybe I was too insistent, too competitive, too ambitious to achieve too much in too short a period of time, and anyway I couldn’t have changed.”