When coming up with villains, you usually want someone who poses a real threat to the story’s heroes. Few things are as important to a story as making the conflict seem like something’s at stake. But if you make a villain or the threat too strong, it can become too abstract or nebulous.

Most villains are roughly as powerful as the hero. If your hero is a spy or a martial artist, the villain may well be a spy or a martial artist. Many of the best villains are the evil equivalents of their heroes — Zod to Superman, Prometheus to Batman — and there’s a special satisfaction to this kind of pairing.

Sometimes, a villain is weaker than the hero. This was often the case in classic super-hero stories, with their Captain Boomerangs and Stilt-Mans. Sometimes the best pairings are mismatched, like a strong hero against a smart villain, or vice versa.

Of course, many of the best villains are more powerful than the hero. That’s why the Kingpin works as a Daredevil villain, because the Kingpin isn’t simply strong; he’s the wealthy boss of a criminal empire.

One of the more interesting aspects of the Transformers — though sadly rarely explored — is that the Autobots were implicitly the underdogs. They transformed into cars. But the Decepticons transformed into weapons. Sure, the Autobots won, again and again. But by their very nature, the Decepticons had the upper hand.

But we’re still talking about pairings on roughly the same level. Let’s get a little more creative here.

The Kardashev scale is a way of measuring hypothetical civilizations. A Type I civilization is capable of utilizing all of the resources of its planet. A Type II, its star. A Type III, its galaxy. Some have proposed a Type IV, which can control its universe, or a Type V, which can control multiple universes. We’re still a Type 0 civilization.

Some villains are so strong that they register on the Kardashev scale.

In super-hero comics, there’s an odd and unsatisfying tendency to jump from Type 0 — such as the villains discussed above — to Type IV. Villains are so often remaking the entire universe. The Anti-Monitor was a Type V villain, unmaking DC’s multiverse. Thanos, with the Infinity Guantlet, was a Type IV. Hal Jordan, in Zero Hour, was a Type IV villain (since he was only unmaking a single universe, the DC multiverse having been condensed to a single universe). Again and again, we hear of unmaking existence… as if that could be anything but an abstract threat. Yet there’s an odd lack of middle ground, between Type 0 and Types IV-V. This oddity is even stranger when you consider how bizarre it is that someone with recognizably human patterns of thought and motivation could ever achieve a Type IV level of power… let alone leap to this level directly from Type 0.

A few examples do occupy this middle ground. There’s the Sun-Eater, from Legion of Super-Heroes — although he’s usually depicted as instinctive and thus isn’t much of a villain per se. The Death Star’s a Type I menace, capable of blowing up planets with a single blast.

Type I and Type II villains offer plenty of cosmic threat. There’s no need to go beyond this, and doing so tends to make the already mind-boggling threat feel oddly impotent. Imagine if the Death Star could blast whole galaxies apart. How would we even process that, as readers?

Of the Type I villains, two of the most classic are planet-eaters: Galactus and Unicron.

It’s said that when Jack Kirby and Stan Lee, in 1966, created Galactus as a foe for the Fantastic Four, their idea was to up the ante by having the super-hero team battle a god. It’s telling that they didn’t create a Type IV (or Type V) villain, which would be closer to a monotheistic creator-god. Instead, they came up with a giant purple humanoid alien with Caucasian skin and (originally) a big “G” on his chest.

Galactus doesn’t literally eat planets. Instead, he sets up giant alien machinery that sucks the “life force” out of planets, killing everything on them and leaving them barren.

Of course, the Fantastic Four defeated Galactus, and it took years before comics took advantage of the obvious drama of depicting Galactus actually successfully consuming a planet. (The first full-length depiction of this occurred in Galactus the Devourer #1, Sept 1999.)

Among super-hero comics fans, Galactus is often revered — largely because a planet-eating was such a cool. But as a planet-eater, he left much to be desired. His anthropomorphism let readers comprehend him as a threat, but it also made him seem more than a little ridiculous in retrospect.

So when it came time to update Galactus for Marvel’s Ultimate Universe (in the 2004-2006 Ultimate Galactus trilogy), writer Warren Ellis stripped the planet-eater of his absurd anthropomorphic aspects. This new Galactus, called Gah Lak Tus, was a swarm of mechanical devices with a collective mind. While this version deprived readers of a giant humanoid villain, rendering the planet-eater more abstract, this new Galactus wasn’t so abstract that it wasn’t dramatic. Indeed, there was something frightening in its cold-minded practicality and technological realism… even if it didn’t make as good a visual.

The 2007 film Fantastic Four: Rise of the Silver Surfer took a less successful path, reimagining Galactus as a kind of cosmic cloud. This avoided the anthropomorphism of the original, which would have been hard to depict convincingly in film, yet was far more abtract and less successful than Ultimate Galactus.

But before either of these reimaginings, 1986′s Transformers: The Movie offered a rival planet-eater in Unicron.

This version wasn’t humanoid at all. Instead, it looked like a ringed mechanical moon, or a small planet, with a giant maw.

And it didn’t use weird technology to suck the life force out of a planet, like some kind of cosmic vampire. No, Unicron ate a planet literally.

Long before the first convincing depiction of Galactus successfully devouring a planet, Transformers: The Movie opened with a mostly silent sequence in which we see a planet filled with mechanical lifeforms consumed by Unicron. We watch as characters try to flee, only to get sucked into the villain along with the rest of their civilization.

Moreover, we follow the pieces of the planet into Unicron, where we see this planet-devourer’s digestion process. Chunks of the planet — and its inhabitants — get metabolized. At the end of the sequence, we watch as resulting energy flows through Unicron, rippling out to the planet-eater’s rings. We then pull back and watch as it floats off, through the empty space where a planet and an entire civilization once was.

It’s a great way of establishing Unicron’s threat. In fact, it’s probably one of the most dramatic openings to a story ever.

Unicron’s established before any of the other Transformers. And the first thing we see him do is destroy and metabolize an entire planet.

It’s not too much to say that this opening sequence out-does the best Galactus sequence. It’s that good.

As a Type I villain, Unicron avoids the anthropocentrism of Galactus, yet manages to be even more menacing. Unicron’s mouth gives the viewer its only anthropocentric element, and even that’s closer to a leech’s mouth than a human one. And how poetic is it that the one identifiable animalistic feature of Unicron’s design is his mouth? The effect is to make Unicron seem less human and more like a force of nature.

But while Unicron solves the problem of Galactus’s anthropocentrism, Unicron offers a far more imposing visual than either Ultimate Galactus or the 2007 movie Galactus.

The parallels between Galactus and Unicron go far beyond the fact that both eat planets. One of the problems of villains who register on the Kardashev scale is that it’s hard to come up with a way to defeat them. The likelihood of a deus ex machina resolution increases proportionately with the villain’s threat.

That’s the case with Galactus’s first appearance, in which the Fantastic Four defeats Galactus with a tiny, hand-held device called the Ultimate Nullifier. As silly as Galactus can be, the Ultimate Nullifier is worse.

Transformers: The Movie is a little better, in that the mystical Matrix is established almost from the beginning. But still, once the Matrix is opened (or activated), it blows up Unicron, as if it’s automatic.

Another problem the two villains share is that they’ve been the subject of some rather silly revisions over time. Part of the reason for this is an obvious limitation in human thinking. Logically, a Type I villain is simply a planet-eater and has no deeper connection with the universe or with reality than any planet would. But the human mind isn’t built to imagine Type I concerns. It’s far too easy for a Type I villain to slide mentally into a Type IV villain, or to acquire Type IV attributes.

So Galactus has been retconned to be an explorer from a universe that preceded the Big Bang, who survived his universe’s destruction, somehow bonded with our universe’s essence and gestated until he took the form with which we’re familiar. It’s an absurd origin, especially since it’s hard to imagine anything connected with the universe being only slighter larger than a human or an ant, at least compared with the vastness of galactic clusters. Again and again, Galactus has been treated as a mystical force, important not only to Type I concerns but to the entire universe.

Similarly, Unicron was retconned to be the embodiment of Chaos whose origins go back to the beginning of the universe. His twin, Primus, the incarnation of Order, is the originator of the Transformers. Supposedly, only one copy of Unicron and Primus exist in the entire multiverse, to which they’re said to be essential. This would make Unicron a Type V villain.

It’s easy to see where these changes originate. It’s tempting to want to add importance to a successful villain (especially one rarely used), and it’s easy to add Type IV traits to a Type I character, considering both are equally unimaginable from a human perspective. Still, it’s absurd to think that anything important to the structure of the universe would be planet-sized (or far less, in the case of Galactus), nor preoccupied with eating something so small, nor recognizably good or evil.

But this does illustrate the clear difficulties of even imagining villains on this scale. But as the popularity of both Unicron and Galactus illustrate, the rewards for success can be great too.