Before there was R, there was S. R was modeled on a language developed at AT&T Bell Labs starting in 1976 by Rick Becker and John Chambers (and, later, Alan Wilks) along with Doug Dunn, Jean McRae, and Judy Schilling.

For more on the history of S, see this interview with another of the creators of S, John Chambers.

Source: The history of R’s predecessor, S, from co-creator Rick Becker