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.
At last week's useR! conference, Rick Becker gave a fascinating keynote address, Forty Years of S. His talk recounts the history of S's genesis and development, using just 3MB of disk on an Interdata 8/32. Rick's talk includes numerous tidbits that explain many characteristics of R, including the philosophy behind the graphics system and the origin of the arrow <- assignment operator in R. The story is also coloured with anecdotes from various other luminaries at Bell Labs at the time, including John Tukey (the pioneer of exploratory data analysis and the inventor of the words "software" and "bit"), and Kernighan and Ritchie (who were upstairs designing Unix and the C language at the same time S was being developed).
Here's Rick's talk, with an introduction by Trevor Hastie. (Many thanks to Microsoft for recording and making the video available.)
For more on the history of S, see this interview with another of the creators of S, John Chambers.