I know of Shannon’s work with entropy, but lately I have worked on succinct data structures in which empirical entropy is often used as part of the storage analysis.
Empirical entropy (as I understand it) is not really different from Shannon’s entropy, except that it is point-wise defined for every string, instead of being defined in a probabilistic setting for a source of strings. Therefore I could credit Shannon for the work, but who did first describe, name, and use it?