She died Saturday, said the show's New York-based production company, TeleNext Media Inc., which didn't say where she died or what was the cause of her death.
Wagner opened "As the World Turns" when it premiered on April 2, 1956, with the words: "Good morning, dear." She held the Guinness World Record for playing the same role on television for the longest amount of time, 54 years, TeleNext Media said.
"All of us at 'As the World Turns' are deeply saddened by Helen's passing," executive producer Christopher Goutman said in a statement. "She is loved by generations of fans, and while we will miss her greatly Helen will always remain the heart and soul of 'As the World Turns."'
While Wagner, who was born in Lubbock, Texas, was seen less often in later decades, no other network television performer came close to her run playing a single character.
She was still part of the cast, though with a small presence, in December 2009, when CBS announced that "As the World Turns" was being canceled and its last episode would air in September 2010.
Her final appearance aired April 5, in an episode in which Julianne Moore, a series regular in the 1980s whose two half-sister characters played Wagner's granddaughters, returned for a guest walk-on. The episode was taped in March.
"As the World Turns" was the first daytime TV drama to run a full half-hour rather than 15 minutes. It rose to No. 1 in the daytime ratings and, in the 1970s, was expanded to an hour.
In a 1968 New York Times interview, Wagner called Nancy "a tentpole character."
"Nothing ever happens to Nancy," Wagner said. "She's the one the others come and talk to."
The many fans who liked Nancy/Wagner came and talked to her, too. She told the Times in 1977 that a woman once ran up and kissed her as she shopped at a supermarket.
"She said, 'Oh, Nancy, I've loved you so long I really must kiss you again,' but at that point I managed to escape," Wagner recalled.
Real life intruded on the show in historic fashion on Nov. 22, 1963, when "As the World Turns" was still performed live on air. Wagner's character was talking about upcoming Thanksgiving plans ("I've thought about it, and I gave it a great deal of thought ...") when the broadcast was interrupted mid-sentence with a "CBS News Bulletin" sign.
Viewers then heard Walter Cronkite announcing that President John F. Kennedy had been shot in Dallas. The actors themselves weren't told at the time.
In a 1998 Associated Press interview, Wagner said she wished her character hadn't receded into the background in later years while most of the plot developments happened to the younger characters.
"I don't like the making of Nancy into only an extra figure at parties," she said. "She is too dynamic a person to be made into a ghost."
Still, she loved the storytelling of daytime television and remembered the maze of complex plots from decades earlier, including her own.
Don MacLaughlin, who played Nancy's first husband, Chris Hughes, died in 1986 at age 79, not long after the show celebrated its 30th anniversary with a special program devoted to Chris and Nancy Hughes' 50th wedding anniversary.
Chris' death was then written into the plotline, and Nancy later married a detective named Dan McClosky, played by Dan Frazer. McClosky's battle with Alzheimer's disease gave Wagner/Hughes a meaty problem on-screen for a few years, but the producers eventually killed him off, too.
Wagner, born in 1918, studied drama and music at Monmouth College in Illinois, graduating in 1938. She appeared on Broadway in the 1940s, including a small role in the musical "Oklahoma!" and in off-Broadway and summer stock productions.
In 2002 Wagner received a plaque on the Buddy Holly Walk of Fame in her hometown, TeleNext Media said, and in 2004 she was awarded a Lifetime Achievement Award from the National Academy of Television Arts and Sciences.
Before gaining her "As the World Turns" gig, she also appeared on early TV shows such as "The Philco Television Playhouse" and a series called "The World of Mr. Sweeney."
She married producer Robert Willey in 1954, and over the years he served as her manager and agent as well as producing some of her stage appearances.