Janet Leigh in Alfred Hitchcock’s “Psycho,” Sigourney Weaver in Ridley Scott’s “Alien.” Courtesy of Paramount Pictures and Twentieth Century Fox.

“Mother’s interrupted the course of our journey. She’s programmed to do that should certain conditions arise.”—Dallas (Tom Skerritt)

40 years ago today, Ridley Scott’s horror classic, “Alien,” went into wide release across the United States. It was a fitting date for the film to launch, considering that on the same day nearly two decades prior, another landmark of the genre opened in Boston, Chicago and Philadelphia, following its June 16th premiere in New York City. That film was Alfred Hitchcock’s “Psycho,” and it changed cinema in ways few pictures ever have. Though Scott credits another game-changer, 1977’s “Star Wars,” as the lightning bolt that set his imagination ablaze, I’d argue that “Psycho” is the black-and-white yin to “Alien”’s red-blooded yang. They are the perfect double bill in countless provocative ways, a fact I never fully realized until my recent screening of the film on a glorious 35mm print at the Chicago Critics Film Festival. Both thrillers offer a master class in misdirection, taking pleasure in gradually revealing their secrets, one by one, until the full truth of their narratives is revealed. This storytelling approach is reflected in each of their opening credit sequences, where the title first emerges in a fragmented, unreadable state until it is completed.

Another notable aspect of these credits is the order of their cast lists. Though Janet Leigh is not top-billed, as is often stated, she was the actor most prominently featured on the “Psycho” poster. When her name does arrive onscreen, it is saved for last, printed in big lettering next to her character identity “as Marion Crane.” Tom Skerritt, however, is top-billed in “Alien,” and like Leigh, does appear to be the main protagonist for the film’s first act. His character, Dallas, is the familiar leading man archetype, a ship captain who does what he believes is right, even if it means bending the rules. Marion is similarly lawless in her actions, stealing money from her boss in a last-ditch stab at happiness. It is the flawed judgment of Marion and Dallas, above all, that dooms them in the end. Whereas her journey is a lone one on the road bound for Fairvale, California—and her boyfriend, Sam (John Gavin)—Dallas is soaring through outer space while aboard the Nostromo, accompanied by his fellow crew members as they head home. We first see them awakening from “hypersleep,” just as our initial view of Marion and Sam is during the final moments of their midday rendezvous in bed. Ironically, the person that rises out of the cryosleep chamber before all the other characters, executive officer Kane (John Hurt), also ends up being the first to die.

The most malevolent word in “Psycho” and “Alien” is one that, in most other cases, conjures a sense of warmth and comfort: “Mother.” It is the invisible presence that haunts every corner of the claustrophobic setting, where our heroes find themselves increasingly clamped in their own “private traps.” Mother manifests itself in characters whose trustworthy appearance and demeanor are nothing more than an elaborate façade. Norman Bates (Anthony Perkins), owner of the motel where Marion stays, and Ash (Ian Holm), science officer of the Nostromo, are each controlled by Mother, who considers any human interfering with her plans as “expendable.” The scene where Ash is revealed to be a machine is reminiscent of the climax in “Psycho,” where the knife-wielding Mother Bates turns out to be Norman in disguise, acting as no less an android and stopped in the nick of time before “she” can kill again. In “Alien,” Mother is the name of Nostromo’s HAL-esque computer system (voiced by Helen Horton), tasked with hiding the true purpose of the ship’s mission from its crew while using Ash as a pawn. Neither Marion nor the crew want their journey disrupted by, respectively, a night at the Bates Motel or a distress signal from a nearby moon. Yet they’re forced to take this diversion since it promises to be a crucial step toward reaching their destinations.

Remnants of a troubling, cyclical past can be detected on the moon, LV-426, which is explored by crew members in a hypnotic, near-wordless sequence that mirrors the secret investigation undertaken by Lila Crane (Vera Miles) of the Bates house toward the end of “Psycho.” Here we find the seated carcass of our monster, which has found new life thanks to its current host. The impregnation and eventual demise of Kane is every bit as violating as the killing of Marion in its sexual imagery. During my interview with documentarian Alexandre O. Philippe—who dedicated an entire film, “78/52,” to analyzing the infamous shower scene—I spoke of how Norman’s stabbing of Marion is lensed like a rape, with the phallic knife penetrating its nude victim. Though I have yet to see Philippe’s upcoming doc, “Memory: The Origins of ‘Alien,’” I imagine he must’ve noted parallels between Hitchcock’s shower murder and Scott’s equally notorious chest-burster scene, where a phallic alien creature explodes out of Kane’s body before scurrying away. These shocking instances of violence occur about a third of the way through each story and heighten the tension during all that follows. The gore lessens considerably with every subsequent death, yet the trauma triggered by our vivid memory of the earlier scene never fades. How appropriate that the fully grown alien’s first fatal blow is preceded by the shower-like trickling of water, enjoyed by technician Brett (Harry Dean Stanton), with his mouth agape.

Fans of the “Alien” franchise tend to forget just how little Sigourney Weaver’s iconic heroine, Ripley, registers during much of its first installment. She starts out appearing to be no more important than the rest of the ensemble—her first appearance occurs during a casual cut in a group scene—and comes across as villainous when ordering Dallas not to bring the infected Kane back onto the ship (Dallas disobeys, naturally). In the director’s cut, Ridley is slapped by navigator Lambert (Veronica Cartwright, star of Hitchcock’s “The Birds”), who is outraged at her refusal to aid in their crew mate’s return. It’s only after Dallas disappears in the second act, vanishing after a sudden cut evocative of Martin Balsam’s swift exit from “Psycho,” that Ripley starts to dominate the screen space. She’s a towering presence when perched in the foreground of the frame, shouting over the protests of engineer Parker (Yaphet Kotto) and effectively shutting him up in the process. By the time the film has reached its final act, Ripley is the ship’s lone survivor, along with her cat. Traces of Hitchcock’s self-aware voyeurism emerge as Ripley readies herself for a well-earned hypersleep, after her escape in a shuttle from the self-destructing Nostromo. Her scantily clad state makes her appear vulnerable for the first time, just as an ingeniously camouflaged alien rears its ugly head in one of the all-time great jump scares. Suddenly, Ripley finds herself as confined as Marion was in the shower, with her back up against the wall and a predator on the prowl mere inches away.

If Dallas is the Marion of “Alien,” then Ripley is its Lila, though she has no need for a man like Sam to save her. When she softly sings “You Are My Lucky Star” (famously belted by Princess Leia’s mother in “Singin’ in the Rain”) to keep her sanity afloat while smoking the alien out of its hiding place, she is singing about herself. She is her own hero from the very beginning, where she prioritized the well-being of her crew even when her methods were unpopular. The finale of “Alien” could be interpreted as an empowering inverse of the shower scene, with the cornered woman fighting against her attacker. Her full-throated scream is not one of surprise or surrender. It is the cry of a warrior unwilling to go gently into that good night. Even Mother gets owned by Ripley’s fury during a crowd-pleasing moment that foreshadows Weaver’s gloriously badass retort to the alien queen in the film’s first and only worthy sequel, James Cameron’s “Aliens” from 1986. After the computer fails to cooperate, Ripley exclaims, “You BITCH!”, before smashing its monitor with a flamethrower. A star was indeed born here in the form of Weaver, who went on to deservedly earn a Best Actress Oscar nomination for “Aliens,” thus cementing her cinematic immortality. As for the other “Alien” knock-offs, consider them all nightmares endured by Ripley in cryosleep, as suggested by her unnerving dream near the start of “Aliens.” There’s no reason not to believe that she and Newt have safely made it home, just as there’s every reason to assume the “Psycho” sequels were dreamed up by Norman while serving his life sentence. After all, as Ripley can no doubt attest, it can get boring talking to Mother all day.

“Alien” is available on a 40th anniversary Blu-ray edition, while “Psycho” can also be found on Blu-ray.