Jorma J. Rissanen (October 20, 1932 - May 9, 2020) has passed away at his residence in Los Gatos, CA.  Dr. Rissanen's seminal contributions to Information Theory include the formulation of the Minimum Description Length (MDL) principle, and the invention of Arithmetic Coding.  He made important contributions to information theory as well as many other fields.  His landmark work was fundamental to the field of source coding.  He was the Shannon Award winner in 2009 and received multiple paper awards including the IT paper award.  More information on Dr. Rissanen's contributions can be found in the proceedings of his 75th birthday workshop. 

Read more at the San Jose Mercury News , and the announcement of his passing from the Helsinki Institute for Information and Technology.