LV-426, also known as Acheron, is the name of the planet where the Alien was first encountered by humans in the movie Alien (1979) of the Alien Series.

The planet is just short of Zeta II Reticuli, which is beyond the Outer Rim. The atmosphere consisted of nitrogen, crystalised carbon dioxide, and methane, as well as some other trace elements. The surface is rock, lava-base, and temperature is deep cold, well below the line.

The Nostromo intercepted a transmission of unknown origin from this planet in 2122, which its seven crewmembers were obligated to investigate, interrupting their journey to Earth with a raw ore shipment. The transmission they received was an acoustical beacon repeating at 12-second intervals, emanating from a derelict spacecraft of alien origin. Inside the derelict, they discovered an enormous alien life form, long-dead and fossilized to its chair behind a large telescopic structure, from which the transmission originated; what the crew first interpreted as an SOS, would be deciphered later by the Nostromo's computer Mother as a warning message.

Instead of heeding the warning, they instead explore deeper into the ship, finding the massive egg chamber. When an organism dubbed, the 'facehugger', attaches itself to one of the unwary crew, they foolishly bring it back aboard their ship, which was in violation of the company science division basic quarantine law of the ICC. This effectively sealed the fate of the ship, the cargo and the it's seven member crew.

In Aliens (1986), terraformer colonists working with Weyland-Yutani Corporation set up large atmospheric processors to make the air breathable. They improved the temperature and made the planet "inhabitable" to human life, establishing a colony called "Hadley's Hope". The colony consisted of approximately sixty to seventy families, with a population of approximately 158. The Xenomorphs were re-discovered by the Jorden family who foolishly brought a facehugger from the Derelict and as a result, the Xenomorphs conquered the colony and made Acheron the new homeworld of their short-live empire.

At the end of Aliens, the colony and The Derelict were destroyed by a thermonuclear meltdown during an unsuccessful attempt by UA Colonial Marines to retake Hadley's Hope from the aliens led by their queen whose hive was headquartered in the colony's Atmosphere Processor. Whether or not the site was recolonized is unknown.