Gellert came with his family to the USA in 1906 from his native Hungary. His early anti-war cartoons appeared in a Hungarian socialist publication Elöre. He made contact with the editorial group at The Masses, and produced illustration work for Liberator.

After the War in which he refused to fight he became a staff artist at The New Yorker and, in 1926, joined the board of the New Masses. He was active wherever censorship and destruction threatened art that didn't suit Government or Capital.

He produced several notable murals, and was active as a political activist until his death in Freeborn, New Jersey in 1985. There is a detailed account of his life in the Graphic Witness website.

Many thanks to Michael T. Ricker who has sent me scans of the artist's work