"Irises," Vincent van Gogh, 1889.
We all know van Gogh, so I won't go into his history, except to note that he painted this during his time in a mental hospital after a period of depression and self-harm. This was a depiction of irises in the asylum's garden, and it seems van Gogh thought of it only as a preliminary sketch. His brother Theo saw it as a beautiful work and submitted to a show where it won acclaim.
It's influenced by Japanese ukiyo-e art, and by van Gogh's striving for a world without pain or tragedy. Sadly, his life would end just over a year after this was completed.
From the Getty Museum, Los Angeles