Life with Unix says: Wrote lex, tbl, refer, —ms macros, uucp and portable C library, precursor to stdio.

A Research Unix Reader says: Mike (Michael E.) Lesk, with a prescient market instinct, made text formatting accessible to the masses with the generic macros — ms, which were to troff what a compiler is to assembly language. He rounded out -ms with the preprocessors tbl for typesetting tables and refer for bibliographies. He also made the lex generator of lexical analyzers. Eager to distribute his software quickly and painlessly, Mike invented uucp, thereby begetting a whole global network. Over the years, often helped by Ruby Jane Elliott, he initiated fascinating on-line audio, textual, and graphical access to phone books, news wire (apnews, v8), weather (v8), and UNIX instruction {learn, with Kernighan, v7).