According to Wikipedia's article on SLAM, the original idea came from Randal Smith and Peter Cheeseman (On the Estimation and Representation of Spatial Uncertainty [PDF]) in 1986, and was refined by Hugh F. Durrant-Whyte and J.J. Leonard (Simultaneous map building and localization for an autonomous mobile robot) in 1991.
However, neither paper uses the term "SLAM". Where (and when) did that term come from? Was there a particular author or whitepaper that popularized it?