She was persistent to the point of badgering. One White House press secretary described her questioning as "torture" and he was one of her fans.
Her refusal to conceal her strong opinions, even when posing questions to a president, and her public hostility toward Israel, caused discomfort among colleagues.
In 2010, that tendency finally ended a career which had started in 1943 and made her one of the best known journalists in Washington. On a videotape circulated on the Internet, she said Israelis should "get out of Palestine" and "go home" to Germany, Poland or the United States. The remark brought down widespread condemnation and she ended her career.
In January 2011, she became a columnist for a free weekly paper in a Washington suburb, months after the controversy forced her from her previous post.
In her long career, she was indelibly associated with the ritual ending White House news conferences. She was often the one to deliver the closing line: "Thank you, Mister. President" four polite words that belied a fierce competitive streak.
Her disdain for White House secrecy and dodging spanned five decades, back to President John Kennedy. Her freedom to voice her peppery opinions as a speaker and a Hearst columnist came late in her career.
The Bush administration marginalized her, clearly peeved with a journalist who had challenged President George W. Bush to his face on the Iraq war and declared him the worst president in history.
After she quit UPI in 2000 by then an outsized figure in a shrunken organization her influence waned.
Thomas was accustomed to getting under the skin of presidents, if not to the cold shoulder.
"If you want to be loved," she said years earlier, "go into something else."
There was a lighter mood in August 2009, on her 89th birthday, when President Barack Obama popped into in the White House briefing room unannounced. He led the roomful of reporters in singing "Happy Birthday to You" and gave her cupcakes. As it happened, it was the president's birthday too, his 48th.
Thomas was at the forefront of women's achievements in journalism. She was one of the first female reporters to break out of the White House "women's beat" the soft stories about presidents' kids, wives, their teas and their hairdos and cover the hard news on an equal footing with men.
She became the first female White House bureau chief for a wire service when UPI named her to the position in 1974. She was also the first female officer at the National Press Club, where women had once been barred as members and she had to fight for admission into the 1959 luncheon speech where Soviet Premier Nikita Khrushchev warned: "We will bury you."
The belligerent Khrushchev was an unlikely ally in one sense. He had refused to speak at any Washington venue that excluded women, she said.
Thomas fought, too, for a more open presidency, resisting all moves by a succession of administrations to restrict press access.
"People will never know how hard it is to get information," Thomas told an interviewer, "especially if it's locked up behind official doors where, if politicians had their way, they'd stamp TOP SECRET on the color of the walls."
Born in Winchester, Ky., to Lebanese immigrants, Thomas was the seventh of nine children. It was in high school, after working on the student newspaper, that she decided she wanted to become a reporter.
After graduating from Detroit's Wayne University (now Wayne State University), Thomas headed straight for the nation's capital. She landed a $17.50-a-week position as a copy girl, with duties that included fetching coffee and doughnuts for editors at the Washington Daily News.
United Press later United Press International soon hired her to write local news stories for the radio wire. Her assignments were relegated at first to women's news, society items and celebrity profiles.
Her big break came after the 1960 election that sent Kennedy to the White House, and landed Thomas her first assignment related to the presidency. She was sent to Palm Beach, Fla., to cover the vacation of the president-elect and his family.
JFK's successor, Lyndon Johnson, complained that he learned of his daughter Luci's engagement from Thomas's story.
Bigger and better assignments would follow for Thomas, among them President Richard M. Nixon's breakthrough trip to China in 1972.
When the Watergate scandal began consuming Nixon's presidency, Martha Mitchell, the notoriously unguarded wife of the attorney general, would call Thomas late at night to unload her frustrations at what she saw as the betrayal of her husband John by the president's men.
It was also during the Nixon administration that the woman who scooped so many others was herself scooped by the first lady. Pat Nixon was the one who announced to the Washington press corps that Thomas was engaged to Douglas Cornell, chief White House correspondent for UPI's archrival, AP.
They were married in 1971. Cornell died 11 years later.
Thomas stayed with UPI for 57 years, until 2000, when the company was purchased by News World Communications, which was founded by the Rev. Sun Myung Moon, leader of the Unification Church.
At age 79, Thomas was soon hired as a Washington-based columnist for newspaper publisher Hearst Corp.
A self-described liberal, Thomas made no secret of her ill feelings for the final president she covered the second President Bush. "He is the worst president in all of American history," she told the Daily Breeze of Torrance, Calif.
Thomas also was critical of the U.S.-led invasion of Iraq, asserting that the deaths of innocent people should hang heavily on Bush's conscience.
"We are involved in a war that is becoming more dubious every day," she said in a speech to thousands of students at Brigham Young University in September 2003. "I thought it was wrong to invade a country without any provocation."
Some students walked out of the lecture. She won over others with humorous stories from her "ringside seat" to history.
In March 2005, she confronted Bush with the proposition that "your decision to invade Iraq has caused the deaths of thousands of Americans and Iraqis" and every justification for the attack proved false.
"Why did you really want to go to war?" she demanded.
When Bush began explaining his rationale, she interjected: "They didn't do anything to you, or to our country."
"Excuse me for a second," Bush replied. "They did. The Taliban provided safe haven for al-Qaida. That's where al-Qaida trained."
"I'm talking about Iraq," she said.
Her strong opinions finally ended her career.
After a visit to the White House, David Nesenoff, a rabbi and independent filmmaker, asked Thomas on May 27, 2010, whether she had any comments on Israel. "Tell them to get the hell out of Palestine," she replied. "Remember, these people are occupied and it's their land. It's not Germany, it's not Poland," she continued. Asked where they should go, she answered, "They should go home." When asked where's home, Thomas replied: "Poland, Germany and America and everywhere else."
The resulting controversy brought widespread rejection of her remarks. White House spokesman Robert Gibbs called them "offensive and reprehensible." Many Jews were offended by her suggestion that Israelis should "go home" to Germany, Poland and America because Israel was initially settled in 1948 by Jews who had survived or escaped Hitler's attempt to kill all the Jews in Germany and in neighboring conquered countries.
Within days, she retired from her job at Hearst.
Nicholas F. Benton, the owner and editor of the Falls Church News-Press, approached her about writing again. Benton, who had published Thomas' column for years when she was syndicated, said Thomas was initially dubious about continuing to write for the free weekly paper, which at the time had a circulation around 25,000.
"She said, 'You don't want me. I'm poison," he said in a telephone interview Saturday.
He responded that he could handle any criticism, and her column started running in January 2011. She continued to write about national issues, from Social Security to the State of the Union address and the low capital gains tax, which she blamed for creating "a bigger divide between the haves and the have-nots, leaving not much of a middle class in America."
Benton said some of his advertisers got threatening calls, but he said he received more positive letters than negative ones by "quite a wide margin." And Benton said she continued to be "sharp as a tack," sometimes asking if she could get her column in after deadline because she wanted to monitor some late-breaking development. She wrote for the paper for a year, until her health prevented her from continuing.
"She was just the kind of person who really did want to fight to the finish," he said of her return to writing.
Associated Press writer Jessica Gresko contributed to this report.
Things to know about Helen Thomas
She spoke to Rowland Hall in Salt Lake City in 2006. Read the article from the Intermountain Catholic: http://tinyurl.com/lfst72a
A first lady once scooped Thomas on a story her engagement. Learn five facts about the trailblazing correspondent: http://ow.ly/n9F9U