Mr. Rain's HAL has become the default reference, not just for the voice, but also for the humanesque qualities of what a sentient machine's personality should be. Just ask Amazon's Alexa or Google Home -- the cadence, the friendly formality, the pleasant intelligence and sense of calm control in their voices evoke Mr. Rain's unforgettable performance. As we warily eye a future utterly transformed by A.I. incursions into all aspects of our lives, HAL has been lurking. To Scott Brave, the co-author of "Wired for Speech: How Voice Activates and Advances the Human-Computer Relationship," HAL 9000 is a mix between a butler and a psychoanalyst. "He has a sense of deference and of detachment," Mr. Brave said, adding that he saw a ripple effect on, for example, the iPhone's virtual assistant.

"I'm sorry, Dave, I'm afraid I can't do that." Even if you've never seen the movie, you know the voice. HAL 9000, the seemingly omniscient computer in "2001: A Space Odyssey," was the film's most expressive and emotional figure, and made a lasting impression on our collective imagination. Stanley Kubrick's epic, a journey from pre-human history to a possible infinity that doesn't need humans at all, is probably the most respected, if not the most beloved, science-fiction film of all time. The story of the creation of HAL's performance -- the result of a last-minute collaboration between the idiosyncratic director Stanley Kubrick and the veteran Canadian actor Douglas Rain -- has been somewhat lost in the 50 years since the film's release in April 1968.