The photos depict street scenes, intimate moments, anonymous portraits -- pictures she apparently never shared with anyone, until John Maloof accidentally stumbled on them.
A few years ago, Maloof, a real estate agent and flea market fan, saw a box of negatives at a Chicago auction house.
"The box I bought was the biggest box they had," said Maloof.
Vivian Maier - Her Discovered Work
"Her storage locker had delinquent payments," explained Maloof. "So what they do is they auction the stuff off."
He bid about $400, hoping to pick up some shots of the city for a book he was writing. What he found in the box has literally changed his life.
"I didn't know how big this would get," said Maloof.
When Maloof posted some of the pictures on a photography website, Maier became an internet sensation.
This month an exhibition of her work opened at the Chicago Cultural Center, but the picture of Vivian herself is still developing.
Born in New York, in 1926, to a French mother, Maier's own tape recordings show her speaking with a slight French accent.
Maloof traced Maier from the name on a film envelope to a 2009 obituary in the Chicago papers that led him to the families she'd worked for.
Like Phil Donahue. Maier took this picture of the talk show host the day he hired her in the late seventies to care for his four sons. She worked for Donahue for nearly a year.
"I met her in a diner as I recall," said Donahue.
In the late eighties, Maren Baylaender's husband hired Maier to care for his disabled daughter.
"I don't think she had a friend," said Baylaender.
Maier never shared her photos with anyone, so would she feel comfortable with them being public?
"I think it would be a shame if this stayed in a dark closet, because we just don't know if she would like it or not," said Maloof. "My mission is to put Vivian in the history books."
Renowned photographer Joel Meyerowitz says she may well belong there. He's co-author of "Bystander: A History of Street Photography."
She's ruthlessly honest about what she sees," said Meyerowitz. "And I think she should be taken seriously."
John Maloof is still working his way through Maier's negatives. He has 90,000 more he hasn't even seen.
Shot by shot, we are coming to know the elusive Vivian Maier, through her own eyes.