Vulcan, Son of Jupiter is like a Marvel Universe comic book movie. All of the correct and most popular names are dropped, but the canon is all screwy because it's a movie series for the masses, not the literal 50-year run of the comic book.
So this is clearly my kind of movie show!

The film begins with a long chunk of text that's a little blurry and has many names and some big words, so you'll have to pause it. It's like a Star Wars opening but in one frame. On Mount Olympus, Mars, Pluto and Vulcan, the sons of Jupiter (Zeus), are being insubordinate. They are all being manipulated by Venus, goddess of "female pulchritude."
On Earth, Venus is playing with Adonis. He's moon-eyed over her. "My love! How long I've awaited you!" She's clearly using him, though. Venus's theme, amusingly, sounds like the music from when Snoopy was behind enemy lines near Marseille on Halloween. The gods are annoyed at Venus, that trollop, and demand her return. Jupiter, standing on a quaint, misty set, summons her back with adorable cartoon lightning bolts.
It is unspoken, mostly, that Jupiter will "tame" this beauty by having her marry one of his sons, either Mars, who is war-like, or Vulcan, who has a metalworks in a cave.

Venus goes to flirt with Vulcan, who is banging some metal with his hammer. It looks like that will be his awesome weapon, but we never see him with it again. She asks, "Are you always alone?" His burly response, "None of your business!" Vulcan says if he's chosen to be her husband, fine, but in the meantime he has his metalwork. Venus leaves, satisfied with that.
Mars, who has sort of a Ted McGinley quality, has been spying and is outraged. He gets into a scrap with Vulcan that is neither interesting nor impressively staged. Jupiter, who appears drunk or bewildered (both?) breaks it up. Their punishment: Mars is deprived of his powers and Vulcan can't work, both for two months. Annoyed, Mars and Venus flee Olympus with some help from Pluto (played by the great Gordon Mitchell from Julius Caesar Against the Pirates).

Vulcan pursues. "The fools!" he shouts. Pluto screws up his arrival, so that he crashes into the sea and washes up on a beach, while Mars and Venus make way safely on horses, heading toward Thrace. On Earth, by the by, these gods are totally mortal.
On the beach, Vulcan, weak, is rescued by many beautiful women, including Edna. They recognize the god immediately. Meanwhile, horned lizard men with long axes slither about. As the girls are taking the god to receive care, Vulcan gets a bad vibe. They're suddenly ambushed! Lizard Men everywhere! The group is easily captured and taken to the Grotto of the Lizard King.

Mars and Venus arrive now at the military camp of Milos, King (?) of Thrace. He is honored, but I think dubious. They know Milos is an enemy of Jupiter, and are there to strike a bargain with him. The Thracian army and its slaves, with Mars, working to overthrow Jupiter from his throne. "I don't accept his orders, but I don't attack him either!" Milos proclaims. Still, he's going to think about it.
Vulcan, in the grotto, is scolded by the Lizard King, who hates the gods. "Monsters we are. You've condemned us, and you will pay!" Above, Jupiter declares he won't interfere, just as Vulcan is being bound for torture.
In the cages, Edna talks with her fellow captives about escape being impossible. "Never has a prisoner succeeded in leaving this cavern of gruesome monsters," the only guy says. They need Vulcan to recover before they can escape. In the meantime, some girls hide the "pygmy-like" Kaho (name?) in a basket. As the comic relief, he protests and complains but is ably tossed into the sea to deliver a message to Neptune.
Kaho stands on a rock, blows his conch, and a Triton immediately blasts out of the water to whisk him to Neptune's soggy lair. There, the little person tells Neptune, a creepy nervous sort, of Vulcan's capture by the Lizard Men.

The Tritons attack The Lizard Men in "The Grotto of Monsters." Vulcan gets free, and easily kills the Lizard King. In the middle of all this, Jupiter announces he will leave his sons on Earth until they specifically fight it out. Pluto does some conniving, as Mars's inside man. Vulcan leaves the grotto with all the freed captives, happy.
At the camp, Mars orders a tower built, a tower that will reach to Olympus. Milos calls it "audacious" and says, "It's madness! Folly!" It will take many, many more men if they want to get this done in less than five months. Mars says to capture some slaves from Sicily, and also "steal the monsters." When the soldiers arrive at the gates of Olympus, Jupiter will lose his powers, and Mars will be King! And Venus will be his queen. Mwa-ha-ha!
NOW Jupiter is annoyed. But, he does nothing. I think he's just waiting for that inevitable fight to make his move. It makes him look incredibly feeble. Also, it's lame.
Vulcan arrives at Neptune's lair, and the sea king is welcoming. There are dancing women. Edna in particular is drawn toward Vulcan. Just then, Mercury, an effeminate sort, arrives. Neptue is annoyed that the dancing was interrupted. Mercury explains to both that Mars is capturing slaves, and planning to overthrow Olympus. Vulcan sets out for Thrace. Neptune gives Mercury a message for dear Jupiter. "From me, he can expect the loyalty of a brother!" (Not that this will have anything to do with anything.)
Despite the urgency, the film meanders as Vulcan is followed by Edna, who loves him. "Don't bother! Don't insist!" is his burly response. He tells her to stay here, it's too dangerous, she's a woman, etc. He conscripts Kaho as his guide. When the little person refuses, he's picked up by his briches kicking and screaming (because he's little, so it's funny). They walk and walk, and he screams and screams. Edna follows. Eventually, the men find horses.
At the camp, construction is underway and the slaves arrive. Mars and Venus are making out, stopping only to laugh as the slaves are whipped into submission.

As Edna jogs behind Vulcan and Kaho, she is suddenly attacked by cannibalistic (?) monkey men! (All the creatures in this world hide by clinging to rocks. If I lived there, I would be checking around every corner for monster men.) She shrieks and calls for help. Vulcan and Kaho turn, and another badly filmed, poorly staged, not at all impressive scrap ensues. Edna is very easily saved. They flee as the reinforcements arrive.

Meanwhile, at camp, a male sibyl predicts... VULCAN! And Kaho and Edna. Everyone is put on alert, and the slaves are extra whipped into submission. One slave I guess tries to plead with Milos, but he's drunk and dismisses her. She curses him with Vulcan's name. "He will come! And you will be destroyed!"
In a touching scene, Edna is crying because she thinks Vulcan doesn't love her, but he says he does and they kiss. The next day, she's kidnapped and brought to the camp. Mars applauds. He says she'll make a great sacrifice to Olympus! Mwa ha ha!
Kaho warns all the prisoners and slaves that Vulcan will give the signal in the morning, and to be ready. Hilariously, that big tower to Olympus is about the size of a normal electrical pylon, but made of wood. Above, Jupiter punishes Pluto for his insubordination. "Return to the realm of shadows!" Venus, jealous, and having declared that she will seduce Vulcan, confronts Edna and slaps her, setting up their climactic fight.
Morning comes. They're about to sacrifice Edna. There's some kind of weird shaman priest dancing around her. Then, the attack! The big epic battle of many extras, clanging and going ooph and uggh, kicking each other to get their swords out of the others guts. The moment we've all waited for. Like the rest of the action in this film, this isn't greatly done, but it is more violent than I expected. Loads of brutal stabbings.
Edna and Venus catfight with whips. Milos gets stabbed to death. Kaho takes a man down and stabs him to death. And, Mars and Vulcan battle it out, with brawn! It's an epic punch battle with some death squeezing. And then, when Vulcan is about to take a dagger to Mars, Jupiter intercedes. Everyone looks skyward as he speaks from above, saying the fight is over. He then summons Mars and Venus back to Olympus for judgment.

Olympus will return to a state of peace, and since Vulcan has found self-fulfillment on Earth, there he will say. Vulcan holds Edna as we fade out to Jupiter's insane, maniacal laughter. MWA-HA-HA! MWA-HA-HA-HA-HA! A happy ending?

Firstly, I think it's neat that they use the Roman versions of the gods. It gives the film expectations that it doesn't live up to at all.
I certainly like that it's nothing but gods, monsters, fighting, etc., but it adds up to not much. There are dozens of subplots introduced and dropped. What does Venus want? Who is Pluto talking to about breaking up Edna and Vulcan? What is Neptune's role? And so on. Similarly, Jupiter's motivations keep changing. He wants one of his sons to marry Venus, he wants them to fight, he won't interfere, he will, he won't, he does. It's irritating!
It's mainly this: The ending is going to be Vulcan versus Mars. Obviously. But that can't happen right away, so it separates the two, and gives Vulcan a bunch of stuff to do, fighting lizard men and one-eyed monkey man cannibals. Mars has this scheme, to give some gravity to the situation, but it amounts to literally nothing. It doesn't change the fact that all Vulcan has to do is punch Mars and it's game over. It's transparent writing. Not that my fiction is any better.
Somehow, even though the film is mostly padding, it isn't ever boring. There's so much going on and creatures keep appearing, so you have a constant anticipation even though nothing is ever delivered.
The film looks like shit. The transfer is fuzzy and murky. The film itself is badly staged and filmed with horrible editing. This was probably hacked by international distributors, like all foreign commercial films of the time, but even still you can just tell that the original edit was not any better. The sets, costumes, locations, everything, all cut-rate. The acting is hammy.
Worst, Vulcan is just a boring hero. He has zero personality. He's got muscles, but no charisma, no presence. The actor, billed as Rod Flash, seems baffled mostly. Oh, we're doing this scene? Uh, okay. Mouth open. He's no Thor or Reg Park as Hercules.
A saving grace is that it can be seen as a superhero show, about on par with Captain America ('90) or Roger Corman's The Fantastic Four. Vulcan and Mars may be mortals, but interesting gods like Neptune and Mercury and especially Pluto (Mitchell is just awesome) show up and do display some special effects superpowers.
That, and because it does follow all the expected beats for a peplum film, makes this entertaining enough. It's a proper B-grade D-film.
Vulcan, Son of Jupiter has 49 votes on IMDb HERE. It can be seen on Pub-D-Hub now and downloaded from archive.org. But both have the Mill Creek Entertainment logo, so I find it dubious.