Short answers, pulled from the story.
El Lissitzky, born Lazar Markovich Lissitzky on the 23rd of November 1890, was a Russian and Soviet artist, designer, photographer, and architect. He is best known for helping develop the suprematist art movement alongside Kazimir Malevich, creating the propaganda poster Beat the Whites with the Red Wedge (1919), designing innovative international exhibition spaces, and developing the Proun series of abstract geometric works.
El Lissitzky was born Lazar Markovich Lissitzky. The name change came in autumn 1919 after Soviet decrees abolished Jewish communal organizations and designated Hebrew letters as anti-communist. Art historian Eva Forgács wrote that he "abandoned his Judaic heritage and became El Lissitzky" at that point. It is unclear whether the name change was a legal act or simply an adopted pseudonym. Art historian Alexandra Shatskikh noted that UNOVIS' nonsense motto "U-el-el'-ul-el-te-ka" may be the source of the name "El."
Prouns, pronounced "pro-oon," were a series of abstract geometric works Lissitzky developed between 1919 and 1920, the name derived from the Russian for "UNOVIS Project." They were his own architectural variant of suprematism, adding the illusion of three dimensions to Malevich's flat, weightless forms. Lissitzky rejected any fixed orientation for them and refused to define them precisely, writing "I cannot give an absolute definition of what Proun is, because the work is not yet dead." Only about twenty-five Prouns have been preserved.
UNOVIS, short for Exponents of the New Art, was a suprematist artists' group co-founded by Malevich and Lissitzky on the 17th of January 1920 in Vitebsk, initially under the name Molposnovis. Members signed collective works with a black square as a seal; Lissitzky used a red square. The group disbanded in 1922 but was described as pivotal in spreading suprematist ideas in Russia and abroad. The first known use of the signature "El Lissitzky" appeared in the group's handmade UNOVIS Miscellany, issued in two copies in March-April 1920.
Beat the Whites with the Red Wedge is a 1919 propaganda poster Lissitzky created during the Russian Civil War. The title, allegedly suggested by Ilya Ehrenburg, is considered a possible counter to the pogrom slogan "Beat the Jews - save Russia!" used by right-wing monarchists and the Black Hundreds. Art historian Maria Elena Versari linked its visual language to Italian Futurism and to a 1918 monument by architect Nikolai Kolli that depicted a red triangle driven into a white rectangular block.
Lissitzky wrote in his 1941 autobiography that 1926 marked the beginning of "my most important work as an artist: the creation of exhibitions." He compared conventional art shows to zoos and designed spaces to make viewers "active participants" rather than passive spectators. His Abstract Cabinet for the Hanover Provinzialmuseum (1926) showed works by Mondrian, Picasso, Mies van der Rohe, and others; it was destroyed by the Nazis in 1937. His Soviet pavilion at the Pressa exhibition in Cologne in 1928 featured a photofresco 3.8 meters high and 23.5 meters long, and he received a governmental medal for the design.