César Vallejo (1892–1938) was born in Peru, and is one of the most important and innovative poets in the Spanish language. He moved to Paris in the 1920s. His most noted works published in his lifetime are Los Heraldos negros (1918) and Trilce (1922), and – at the instigation of his poet wife Georgette – came the posthumous Poemas Humanos (1939).
He was initially buried in Montrouge, although in 1970 his remains were moved – according to his wishes, as the inscription above notes – to the cimetière du Montparnasse, where he could be close to Baudelaire.
'J'AI TANT NEIGÉ
POUR QUE TU DORMES
The above inscription is said to be written by Georgette (1908–84) although there's no way round the fact that translated it reads 'I have snowed so much | So that you can sleep | Georgette': I don't think anyone has as yet suggested a meaning.
ADDENDUM: The Spanish Wikipedia page for Vallejo says the inscription is 'He nevado tanto para que duermas': 'It has snowed...'. Although this is clearly not what is inscribed on the grave, it makes a lot more sense, with the snow being visualised as a shroud. So the 'J'ai' above should probably read 'Il a'.