Jorma Johannes Rissanen (October 20, 1932 – May 9, 2020)[2] was an information theorist, known for originating the minimum description length (MDL) 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.
Most of his PhD work was done remotely as a result and he received his Ph.D. from the Helsinki University of Technology in 1965 with a topic on adaptive control theory.
The work on MDL developed into the more general notions of stochastic complexity (about which he wrote an influential book[4]) and universal coding/modeling.
[8] 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.