Cezanne is considered to be the guiding force & architect of 20th century
painting. He spent most of his life living and working in Southern France
(specifically Provence), an area that hosted some of the world's most
fascinating 19th/20th century painters including Van Gogh, Matisse and Picasso.
Why him? Well, in the simplest terms, his style boiled down to composing
his paintings with geometric brush strokes. Effectively, rather than painting
dots (like Seurat or Pissarro, the Pointillist school of Impressionism) or
thick slabs/swirls of paint (like late Monet or Van Gogh), Cezanne pieced
together squares/blocks that would create an overall view.
That geometrisation is what influenced Braque and Picasso to compose in
the same way but then, rearrange the placement of those "blocks," effectively
what is called cubism.
Doubt this explains it well enough but I'm only a fan, not a true scholar
on the subject.