The Hyperdyne Systems 120-A2 is a fictional robotics appelation used in the Aliens film series. It appeared in the first Alien film in 1979 in the form of the robot known as Ash, but was not provided with its nomenclature until clarified by another android, Bishop, in the 1986 sequel, Aliens.
The Hyperdyne Systems 120-A2 model android was constructed by Hyperdyne Systems as a fully functional synthetic human. Hyperdyne created a 120-A2 unit that was named Ash, which was placed into service to the Weyland-Yutani Corporation. He was assigned to serve as Science Officer aboard the commercial towing vessel Nostromo under the command of Captain Dallas. Neither Dallas nor the rest of the crew were aware that Ash was an android, and as such, were unaware of his true mission. Weyland-Yutani sent Ash on the Nostromo under Special Order 937, which involved the procurement of an alien organism which was believed to originate somewhere in the Zeta II Reticuli System on the Outer rim of the galaxy. All other matters were considered secondary and the crew was expendable.
In 2122, the Nostromo was returning from a job in the Solomons when the ship received a distress beacon coming from a nearby planetoid. They took a drop-ship to the planet's service and discovered the wreckage of a derelict space vessel as well as the fossilized remains of its pilot. The Nostromo's second in command, Kane, was attacked by an embryonic creature which attached itself to his face. Despite all quarantine procedures, Ash allowed Kane back onto the ship so he could analyze the organism. He attempted to surgically remove the creature from Kane's face, but when he made an incision on one of the phalanges, he found that the alien had concentrated acid for blood. He also determined that the so-called "Face Hugger" served as a sort of midwife to another species. It inserted a probiscus into Kane's mouth, which kept his body stable, but also impregnated him with a seed that gestated inside of Kane's chest. The Face Hugger eventually detached itself from Kane and died after serving its biological requirements.
The product of this process grew inside of Kane and adapted some of his physiological characteristics. Using Kane as a birthing chamber, it burst free of his body and quickly grew into a full-sized Xenomorph. Ash deliberately sabotaged the crew's efforts to destroy the creature and Warrant Officer Ellen Ripley eventually discovered the truth about Ash's mission. Ash offered to explain himself to Ripley, but she wouldn't hear it and attempted to warn the rest of the crew about him. Ash grabbed Ripley and threw her against a computer panel on the bridge of the ship. He then began to suffocate her by shoving a rolled up magazine into her mouth. Crew members Parker and Lambert came to Ripley's rescue and Parker bashed Ash across the back of the head with a steel pipe. This caused a malfunction in the android and he began spasming and spinning about in circles, bouncing off the walls of the ship. Parker struck him a second time and partially dislodged his head. It was at this point that everyone learned that Ash was an android. After incapacitating his body, Lambert reconnected his head and vocal processors so they could learn the truth about his mission parameters. Ripley asked him how they could neutralize the alien and Ash plainly stated, "You can't". Frustrated by the uncooperative traitor, Parker finished him off by incinerating the remains. [1]
In the year 2179, Carter Burke told the tale of Ash's malfunction to a more advanced 341-B model named Bishop, who admitted that the A2's were always a bit "twitchy". [2]