Recently, I re-read Clarke's 2001 series (all four books). The books don't have perfect continuity, and he discusses this in his prologues. In the series, the

Recently, I re-read Clarke's 2001 series (all four books). The books don't have perfect continuity, and he discusses this in his prologues. In the series, the "monolith" changed from being a tool of an early, lonely, space-faring race, to an autonomous thinking machine, acting independently.