Short answers, pulled from the story.
Logic Theorist is a computer program completed in 1956 by Allen Newell, Herbert A. Simon, and Cliff Shaw. It is widely described as the first artificial intelligence program, built to perform automated reasoning before the field of AI had even been named.
Logic Theorist proved 38 of the first 52 theorems in chapter two of Whitehead and Russell's Principia Mathematica. For at least one theorem, numbered 2.85 in the source, the program produced a proof more elegant than the one Russell and Whitehead had constructed by hand.
Allen Newell was a RAND Corporation scientist studying logistics and organization theory. Herbert Simon was a political scientist known for his theory of bounded rationality, who later won the Nobel Memorial Prize in Economic Sciences in 1978. Cliff Shaw, also from RAND, was the programmer Newell and Simon described as the genuine computer scientist of the group.
Logic Theorist introduced the concept of reasoning as search through a tree of logical possibilities, and the use of heuristics to trim exponentially growing search spaces. To implement the program, the team also built IPL, a list-processing programming language whose approach later formed the basis of McCarthy's Lisp language.
Newell and Simon presented Logic Theorist at the summer 1956 conference organized by John McCarthy, Marvin Minsky, Claude Shannon, and Nathan Rochester, but the program received a lukewarm reception. Pamela McCorduck wrote that nobody at the conference except Newell and Simon themselves recognized the long-range significance of the work.
The physical symbol systems hypothesis, developed by Newell and Simon, holds that a physical system manipulating symbols can exhibit intelligent behavior. Logic Theorist was the first program to run on hardware as a demonstration of this idea. Simon described the work as solving the mind-body problem by showing how a system composed of matter can have the properties of mind.