Jorma Rissanen
Jorma J. Rissanen (October 20, 1932 – May 9, 2020) was an information theorist, known for originating the minimum description length principle and practical approaches to arithmetic coding for lossless data compression. His work inspired the development of the theory of stochastic chains with memory of variable length. An IBM researcher since 1960, first in Stockholm, Sweden, and then at IBM Almaden in California, Rissanen received his Ph.D. from the Helsinki University of Technology in 1965. He stayed with IBM until his retirement in 2002, with a brief interruption in 1974 as a professor of control theory in Sweden . During that time, he became familiar with the work on algorithmic randomness by Kolmogorov and Martin-Löf, which inspired his work on arithmetic coding and MDL, leading to a stream of ground-breaking publications from the late 1970s to the early 1990s. The work on MDL developed into the more general notions of stochastic complexity (about which he wrote an influential book) and universal coding/modeling. Retired from IBM, he remained professor emeritus of Tampere University of Technology and a fellow of Helsinki Institute for Information Technology. Awards and recognitions. He was awarded the IEEE Richard W. Hamming Medal in  1993, an IEEE Golden Jubilee Award for Technological Innovation from the IEEE Information Theory Society in 1998, the Kolmogorov Medal of the University of London in 2006, and the IEEE Claude E. Shannon Award in 2009. A Festschrift collection, which includes an interview and substantial biographical information, was published by the Tampere University of Technology in honor of his 75th birthday.