12 July 1876
; Quimper, Brittany, France *
05 March 1944
; Drancy / Le Blanc-mesnil, France *
Jacob departed his native Brittany in 1894 to go to Paris, where he lived in extreme poverty but eventually became an important figure in Montmartre during the formative period of Cubism. He was a friend of the Cubist painters Pablo Picasso and Juan Gris and of the poet Guillaume Apollinaire. Jacob converted to Christianity in 1909 and became a Roman Catholic in 1915, but he nevertheless continued to oscillate between extravagant penitence and wild bohemianism until 1921, at which time he retired into semimonastic seclusion at Saint Benoît-sur-Loire. He lived there most of the time, supporting himself by painting, until World War II, when he was interned in the concentration camp at Drancy, near Paris, where he died.