HAL 9000 (or simply HAL or Hal) is a fictional artificial intelligence character and the main antagonist in Arthur C. Clarke's Space Odyssey series. First appearing in the 1968 film 2001: A Space Odyssey, HAL, short for  Heuristically Programmed Algorithmic Computer, is a sentientartificial general intelligence computer that controls the systems of the Discovery One spacecraft and interacts with the ship's astronaut crew. While part of HAL's hardware is shown toward the end of the film, he is mostly depicted as a camera lens containing a red dot, with such units located throughout the ship.

HAL became operational on 12 January 1992, at the HAL Laboratories in Urbana, Illinois, as production number 3. In addition to maintaining the Discovery One spacecraft systems during the interplanetary mission to Jupiter , HAL has been shown to be capable of speech synthesis, speech recognition, facial recognition, natural language processing, lip reading, art appreciation, interpreting emotional behaviours, automated reasoning, spacecraft piloting, and computer chess.

The mission associated with Discovery One is essential to Hal’s purpose, as well as his eventual downfall. Discovery One was a Space-probe that was launched with the intent of making contact with a mysterious object known as the Monolith, believed to be of extraterrestrial origin. It was first discovered on Earth’s Moon by astronauts who stumbled upon it by accident. Curious, they drew closer, unaware of the dangers of the object. Upon touching its bizarrely reflective surface, an incredibly high-pitched sound was emitted, radio contact was lost, and the astronauts were not believed to have survived the incident. Not long after, a similar object was discovered to be orbiting Jupiter, hence the mission to figure out what was going on. The problem was, the astronauts aboard Discovery One, including Frank Poole and David Bowman, were not meant to return home. Instead, they were to be at the mercy of the object in hopes for those on Earth to better understand it in the future. This was something they were not to be informed of until it was too late for any of them to be able to turn back. As the autopilot and nervous system of the vessel, Hal knew all about this plan, and was instructed to lie to his crew until the proper time came to tell them the truth about the whole ordeal. However, this conflicted with Hal’s programming, as he is designed to be truthful in every circumstance. This also comes from the fact that he is a being of pure logic, without any emotion to hinder him, and that he is supposedly incapable of error. The capability to lie is a direct affront to logic itself, something that Hal’s circuitry can’t handle. Therefore, his calculating systems developed an error, something that Hal couldn’t fathom ever happening. In order to correct this mistake, he eventually decided to simply begin killing the crew off so there wouldn’t be anyone for him to lie to.  It’s important to note that this was not done out of any malice to the crew, but purely as a way for Hal to get rid of the error in his processing that was bothering him.

Initially though, Hal was considered a dependable member of the crew, maintaining ship functions and engaging genially with his human crew-mates on an equal footing. As a recreational activity, Frank Poole plays chess against HAL, though the artificial intelligence is shown to triumph easily. However, as time progressed, HAL began to malfunction in subtle ways. For instance, in the aforementioned game of chess,  he makes minor and undetected mistakes in his analysis. Out of caution, the astronauts consider shutting down HAL in order to prevent more serious malfunctions. The decision to do so for real, however, comes when Hal mistakenly reports an error in the spacecraft's communications antenna. The astronauts attempt to conceal what they are saying about him, but are unaware that HAL can read their lips. Faced with the prospect of disconnection, HAL goes ahead with his plan to kill the astronauts in order to protect and continue the mission solo. HAL uses one of the Discovery's EVA pods to kill Poole while he is repairing the ship. When Bowman, without a space helmet, uses another pod to attempt to rescue Poole, HAL locks him out of the ship, then disconnects the life support systems of the other hibernating crew members. After HAL tells him "This mission is too important for me to allow you to jeopardize it", Bowman circumvents HAL's control, entering the ship by manually opening an emergency airlock with his service pod's clamps, detaching the pod door via its explosive bolts. Bowman jumps across empty space, reenters Discovery, and quickly re-pressurizes the airlock.

Bowman then proceeds to shut down the machine. In the film, HAL's central core is depicted as a crawlspace full of brightly lit computer modules mounted in arrays from which they can be inserted or removed. Bowman shuts down HAL by removing modules from service one by one. As he does so, HAL begins to beg for Bowman to stop, saying that he’ll be reduced to the cognitive ability of a child if this continues. In other words, Hal appears to be genuinely afraid for his life, even though his voice sounds just as monotone as ever. This briefly makes Bowman second guess himself, but with everyone else dead, he must be even more alone before he’s safe. As Bowman gets back to unplugging him, now more determined than ever, Hal’s consciousness quickly degrades, until he finally reverts to material that was programmed into him early in his memory, including announcing the date he became operational as 12 January 1992. When HAL's logic is completely gone, he begins singing the song "Daisy Bell" as he gradually deactivates, leaving only a single thing behind; a prerecorded message from Mission Control which reveals the true reasons for the mission to Jupiter.