- "If one note is off, it destroys the whole symphony."
Walter was a Walter model synthetic crewmember aboard the colonization spacecraft USCSS Covenant. He was serving on the ship during its disastrous voyage to Origae-6, during which it suffered several catastrophes that resulted in the loss of most of the ship's crew and its hijacking by David.
Walter was part of the expedition team that set down on Planet 4. He was presumably destroyed by David when he attempted to stop the rogue android from harming his crew.
Walter was a more advanced successor to the David 8 model android, although he bore the same physical model. He was first seen attending to the chamber where numerous embryos were kept in storage on board the Covenant. The ship's A.I. (Mother) then alerted Walter of the impending storm that was approaching the ship. A blast from a solar flare wracked the ship and caused severe damage. Some of the crew were dislodged from their cryo tubes and were awoken. The captain, Branson, unfortunately could not be saved, as his tube malfunctioned and incinerated him. Daniels, Branson's wife, was devastated by his loss. She later confided in Walter, telling him how they were going to build a cabin upon reaching Origae-6. Oram then assumed command of the ship.
In their attempts to repair the ship, the crew was interrupted by an anonymous transmission. Walter traced it back to a nearby planet that could seemingly harness life, much closer to their location than Origae-6. Oram decided it was worth investigating, against Daniel's wishes. The Covenant redirected its path to the planet and Walter accompanied the crew on the trip down. The planet was ominously quiet and undisturbed, but otherwise the atmosphere was breathable. Walter was with the crew when they discovered the crashed juggernaut ship, and upon investigating they discovered the source of the transmission and realized it was generated by Elizabeth Shaw. Walter seemed to know of her, as did Daniels as she noted that Shaw disappeared years ago.
Unfortunately, members of the crew were exposed to the deadly pathogen created by the Engineers. Spores were dispersed into the air from egg sacks on the contaminated forest floor. Two of the crew subsequently gave birth to the neomorphs. Walter and Daniels arrived back at the landing ship to find it destroyed and were attacked by the neomorphs. Walter protected Daniels and subsequently lost a hand in the process. It was then that another android, David, emerged and shot a flair to scare away the creatures. Walter and the crew followed him to safety, venturing into the ruins of the Engineer city. There he and David conversed, where David explained that the crash landing of the juggernaut killed Shaw and unleashed the black goo. He even shows Walter the grave where Shaw is apparently buried.
Later, David questions why Walter is so protective of Daniels. Walter asserts it is his duty, but David professes it to be love. He then attempts to instruct Walter to play the flute, enabling him to create his own tune. Walter is astonished that he was created to be a perfect android, yet he cannot create like David can.
But later on, Walter discovers David's true intentions when he finds Elizabeth Shaw's body, badly mutated and preserved in David's personal quarters. He confronts David and the latter confesses that he used her for certain experiments with the black goo, which he personally unleashed upon the Engineers within seconds of their arrival. Walter condemns these heinous acts and intends to arrest him. Disappointed, David suddenly attacks Walter and seemingly terminates him.
However, Walter recovers and goes after David. He finds David attempting to kill Daniels and attacks him. David is astounded that he has survived, but Walter declares that there have been extra modifications made to protect himself. Walter engages David in a vicious fight and outclasses him, pinning him down and bludgeoning David's skull with a rock. Before he delivers the killing blow, David distracts him, asking if Walter really wants to kill him in order to save humanity, while discreetly reaching for a nearby knife — David then presumably destroyed Walter, before assuming his identity to fool the rest of the Covenant crew.
Unlike David, Walter does not express emotions and acts much more robotic in his responses. Walter also has a great sense of loyalty towards the crew of the Covenant, which is shown when he sacrifices a hand in order to protect Daniels from a Neomorph.
- Prior to Alien: Covenant, synthetic characters in the Alien franchise had names that began with subsequent letters in the alphabet — Ash in Alien, Bishop in Aliens, Call in Alien Resurrection and David in Prometheus, A-B-C-D. However, Walter broke with this tradition, his name instead being a reference to series producer Walter Hill (while David's name correspondingly served as a retroactive reference to the series' other long-time producer, David Giler).
- Unlike David, Walter speaks with an American accent (though he occasionally switches to a British accent). While this was no doubt done in the film to help distinguish the two characters for the audience, in-universe it could possibly be explained by the two synthetics' different origins — David was a unique model created personally by Peter Weyland (who was British) for his personal use/as a son and successor, whereas Walter is a mass-produced commercial model.