Art by Hilma af Klint

Af Klint was painting large-scale abstract works years before Kandinsky, Mondrian, or Malevich, the artists usually credited as abstraction's pioneers, but almost nobody knew it at the time. A committed spiritualist, she made much of her early abstract work through group séances, treating the paintings as messages channeled from spirits rather than personal artistic statements, and she left explicit instructions that the work not be shown publicly until at least 20 years after her death, believing the world wasn't ready for it. That instruction was honored well past its minimum, and it wasn't until a blockbuster 2018-19 retrospective at the Guggenheim, one of the museum's most-visited shows ever, that she was widely recognized as having gotten to abstraction first.