Life with Unix says: Suggested idea of pipes. Wrote tmg. Wrote diff and spell. Research in speech processing on UNIX led to grep.
A Research Unix Reader says: Doug (M. Douglas) Mcllroy exercised the right of a department head to muscle in on the original two-user PDP-7 system. Later he contributed an eclectic bag of utilities: tmg for compiler writing, speak for reading text aloud, diff, and join. He also collected dictionaries and made tools to use them: look (v7, after a model by Ossanna), diet (v8), and spell (v7).