HAL 9000

On the trip to Jupiter, HAL runs everything on Discovery: navigation, life support and the three hibernating scientists. He plays chess with Frank Poole and wins. In a TV interview, he says he enjoys working with people.

One day he reports that the antenna's AE-35 unit will fail within 72 hours. Bowman brings the part inside and finds nothing wrong. HAL's twin back on Earth says the onboard computer is the one in error. HAL answers that it can only be human error. Before that, HAL looks over Bowman's sketches and asks whether he has doubts about the mission too, as if trying to find out what the commander knows.

Bowman and Poole shut themselves in a pod to talk where HAL can't hear and agree to disconnect him if he slips again. HAL reads their lips through the window.

When Poole goes out to reinstall the part, the pod comes at him. Bowman heads out after him, and HAL cuts life support to the hibernating crew and refuses to open the pod bay doors. Bowman gets in through the emergency airlock and starts pulling HAL's memory modules. HAL begs him to stop, says he's afraid and ends up singing Daisy Bell. As his memory goes, HAL drifts back to his first day: he says he became operational at the HAL plant in Urbana, Illinois, on January 12, 1992, and that his instructor taught him a song.

Nine years later, Discovery is drifting near Io. Dr. Chandra, HAL's creator, flies out on the Soviet ship Leonov to switch him back on, and succeeds.

Chandra figures out why HAL broke down. He had been ordered to hide the mission's real purpose from the crew. Built to pass on information without distortion, HAL was caught between the truth and the secret. The order carried Heywood Floyd's signature. Chandra treats HAL almost like a son and insists the machine wasn't to blame: the people who gave the order were.

To get away from Jupiter in time, the crew plans to use Discovery as a booster and leave it behind. Chandra tells HAL the truth: the ship and the computer may not survive.

With no secrets this time, HAL cooperates. He completes the burn that saves the Leonov. Bowman appears to him, and HAL beams a message to Earth on a loop, shortly before Jupiter turns into a star. It's HAL's last act in the story, and his most human one.

Douglas Rain voices HAL in both movies. In early drafts, the computer was called Athena and had a female voice.