Vivian Maier was a nanny as well as an avid street photographer from the 1950s-1990s. However, her incredible photography work wasn't discovered until an auction in 2007 when someone uncovered 10,000 negatives and undeveloped rolls of films of hers.
Her human/society observations are AMAZING. I have to say I also love her use of shadows and her self portraits. Very inspiring.
Photos from here. See more on the Official Website of Vivian Maier.