M. Douglas McIlroy, formerly of AT&T Bell Laboratories and present at the creation of the Unix operating system, offers an authoritative historical summary.
The prime reason for Unix was the desire of Ken [Thompson], Dennis [Ritchie], and Joe Ossanna to have a pleasant environment for software development. The fig leaf that got the nod from … management was that an early use would be to develop a “stand-alone” word-processing system for use in typing pools and secretarial offices. Perhaps they had in mind “dedicated”, as distinct from “stand-alone”; that’s what eventuated in various cases, most notably in the legal/patent department and in the AT&T CEO’s office.
Both those systems were targets of opportunity, not foreseen from the start. When Unix was up and running on the PDP-11, Joe got wind of the legal department having installed a commercial word processor. He went to pitch Unix as an alternative and clinched a trial by promising to make
roffable to number lines by tomorrow in order to fulfill a patent-office requirement that the commercial system did not support.Modems were installed so legal-department secretaries could try the Research machine. They liked it and Joe’s superb customer service. Soon the legal department got a system of their own. Joe went on to create
nroffandtroff. Document preparation became a widespread use of Unix, but no stand-alone word-processing system was ever undertaken.
A history relating groff to its predecessors roff,
nroff, and troff is available in the roff(7)
man page.