"I hope there are many women following me right in this same spot," she said. Well into her 80s, she was a mentor to many young journalists.
Thomas left UPI in May 2000, when the wire service was sold to a company controlled by the Rev. Sun Myung Moon, the Korean founder and leader of the worldwide Unification Church.
Two months later, Hearst News Service hired her as a syndicated columnist, and she returned to the White House for fodder for her columns.
Former President Bill Clinton and his wife, former Secretary of State Hillary Clinton, recalled Thomas' "tough-minded dedication."
"Helen was a pioneering journalist who, while adding more than her share of cracks to the glass ceiling, never failed to bring intensity and tenacity to her White House beat," the Clintons said in a statement.
"... Her work was extraordinary because of her intelligence, her lively spirit and great sense of humor, and most importantly her commitment to the role of a strong press in a healthy democracy."
No question seemed off-limits
Colleagues remember her as a genuinely fearless woman who asked the toughest questions of presidents, no matter their party.
In January 2009, as President George Bush was preparing to leave office, Thomas aimed her editorial guns at him and his administration.
Among her criticisms: that before the September 11, 2001, terror attacks, administration officials ignored "significant early warnings of an imminent strike against the U.S."
In a commentary, she slammed Bush for what she considered his failings, including leading the country "into a senseless war against Iraq, a calamity still under way as he leaves office almost six years after the invasion."
She considered him "the worst president ever."
Thomas embraced the freedoms of a columnist with vigor.
"I censored myself for 50 years when I was a reporter," Thomas told an audience at the Massachusetts of Technology (MIT) in late 2002. "Now I wake up and ask myself, 'Who do I hate today?'"
One afternoon in October 2009, she targeted President Barack Obama's spokesman, Robert Gibbs, during the daily briefing.
Health care reform was being debated at the time, and Thomas asked Gibbs every day whether a public option would be part of the package.
In the back-and-forth that ensued, Thomas said that she already had reached a conclusion but could not get a straight answer from the presidential spokesman.
"Then why do you keep asking me?" Gibbs inquired.
"Because I want your conscience to bother you," Thomas replied.
The room broke into laughter as Gibbs turned red.