Tim Russert, a political lifer who made a TV career of his passion with unrelenting questioning of the powerful and influential, died of a heart attack Friday in the midst of a presidential campaign he had covered with trademark intensity.

Read: Russert Remembered

Tom Brokaw, the former anchor of "NBC Nightly News," came on air during a special report Friday afternoon and said Russert's death came during a political campaign that "he loved." He called Russert a "beloved colleague" and "one of the premier journalists of our time."

"And I think I can invoke personal privilege to say that this news division will not be the same without his strong, clear voice," Brokaw said. "He'll be missed as he was loved, greatly."

The network said on its Web site that Russert had been recording voiceovers for this Sunday's "Meet The Press" when he was stricken.

Attempts to resuscitate him were unsuccessful. MSNBC reported on its Web site that Russert’s physician, Michael Newman, said cholesterol plaque ruptured in an artery, causing sudden coronary thrombosis. An autopsy revealed that he also had an enlarged heart, Newman said.

Russert had been diagnosed with asymptomatic coronary artery disease, which he was controlling with medication and exercise, the doctor said.

Russert is survived by his wife, Maureen Orth, a writer for Vanity Fair magazine, and his son, Luke. Russert had recently returned from Italy, where his family had been celebrating his son's graduation from Boston College.

The network announced that Brokaw would anchor a special edition of "Meet the Press" on Sunday, dedicated to Russert.

NBC released a statement Friday afternoon, calling Russert's passing devastating.

"We have lost a beloved member of our NBC Universal family and the news world has lost one of its finest. The enormity of this loss cannot be overstated. More than a journalist, Tim was a remarkable family man. Our thoughts and prayers are with his wife, Maureen, their son, Luke, and Tim’s entire extended family," Jeff Zucker, NBC Universal's chief executive officer, said in a statement.

NBC colleague Brian Williams said, "He was a giant in our company, in our lives, and in the combined fields of journalism and politics."

Russert, 58, was a political operative before he was a journalist. He joined NBC a quarter century ago and ended up as the longest-tenured host of the Sunday talk show "Meet the Press." He was also NBC's Washington bureau chief.

He was an election-night fixture, with his whiteboard and scribbled figures, and was moderator for numerous political debates. He wrote two best-selling books, including the much-loved "Big Russ and Me" about his relationship with his father.

Russert, of Buffalo, N.Y., took the helm of the Sunday news show in December 1991 and turned it into the nation's most widely watched program of its type. His signature trait was an unrelenting style of questioning that made some politicians reluctant to appear, yet confident that they could claim extra credibility if they survived his grilling intact.

"I can say from experience that joining Tim on "Meet the Press" was one of the greatest tests any public official could face," said Rep. John Boehner, House Republican leader. "Regardless of party affiliation, he demanded that you be straight with him and with the American people who were watching."

Russert was also a senior vice president at NBC, and this year Time magazine named him one of the 100 most influential people in the world.

He had Buffalo's blue-collar roots, a Jesuit education, a law degree and a Democratic pedigree that came from his turn as an aide to the late Sen. Daniel Patrick Moynihan of New York.

Lawmakers from both parties lined up to sing his praises after his sudden death.

Senate Majority Leader Harry Reid said Russert was "the best in the business at keeping his interview subjects honest."

"There wasn't a better interviewer in television," Sen. Barack Obama, the Democratic presidential contender, told reporters in Ohio.

Republican Sen. John McCain of Arizona, Obama's rival for the White House, hailed Russert as the "pre-eminent journalist of his generation."

Carl P. Leubsdorf, president of the Gridiron Club, an organization of journalists, said, "It was a measure of the degree to which Tim Russert was respected in the journalistic world that he was the first broadcaster elected to membership in the Gridiron Club after the rules were changed in 2004 to end our century-old restriction to print journalists."

He had dozens of honorary college degrees, and numerous professional awards. He won an Emmy for his role in the coverage of President Ronald Reagan's funeral in 2004 and also wrote the best-selling books "Big Russ and Me," in 2004, and "Wisdom of our Fathers," in 2006.

Russert was married to Maureen Orth, a writer for Vanity Fair magazine. The couple had one son, Luke.

Washingtonian magazine also once dubbed Russert the best journalist in town, and described "Meet the Press" as "the most interesting and important hour on television."

In addition to his political ties, Russert was also a sports fan, principally of his hometown Buffalo Bills, but also of the New York Yankees and Washington Nationals baseball teams. He was a season ticket holder of the Nationals since the team moved to Washington from Montreal before the 2005 season.

Russert was elected to the Baseball Hall of Fame board of directors, where he sat with Hall of Fame players Frank Robinson, Brooks Robinson, Robin Roberts and Tom Seaver, Commissioner Allan H. (Bud) Selig, Yankees principal owner George Steinbrenner, Cardinals general partner Bill DeWitt and Royals owner David Glass.

Major League Baseball reported on its Web site that Russert said he was thrilled when he was selected to the Hall of Fame Board.

"Baseball has been central to my life, as a son and as a father," he said at the time. "I am honored to join the Board of the Hall of Fame to help preserve the history of baseball and educate a new generation about the glory of the game."