Are you ashamed of your size? You should be! Compared to Ego The Living Planet or Unicron the planet who turns into a giant robot, you're not only puny and tiny, you're kind of dumb as well. If there's one thing that science fiction teaches us, it's that you need a sun-sized brain to think truly cosmic thoughts. (And to eat other planets for lunch, too.) But which life form in scifi is the hugest (and therefore the smartest)? We've got the answer.
Note: I was almost done compiling this list when I came across this helpful post from Lev Grossman at Time.com, and its equally helpful comments. (Although the person who thought the ship in Farscape was called "Moira" cracked me up.)
Mogo the Green Lantern planet, from Green Lantern. Created by Alan Moore in his classic "Mogo Doesn't Socialize" short comic strip, Mogo is a whole planet wearing a green-lantern ring and defending the galaxy against wrongdoers. He's been brought back in recent issues of Green Lantern Corps. and has actually managed to communicate with the otherLanterns, despite the whole "not socializing" thing. How does he travel around? How does he defend all the planets in his sector of the galaxy? It's not clear to me, but here are some more details, including a link to scans of his first appearance.
Ego The Living Planet, from Thor and various other Marvel Comics. Which sentient planet is bigger, Ego or Mogo? It's hard to say. But I'm going to come down on the side of Ego being more awesome, because he cruises around and acts sleazy — as in one of his most recent appearances, where he falls in love with Earth and tries to seduce the entire planet (which has become sentient). In a smackdown between Ego and Mogo, my money is on Ego, even though Mogo has the magic alien ring. You know Ego would fight dirty, because everything he does is dirty.
The Beast With A Billion Backs from Futurama, "The Beast With A Billion Backs." The second direct-to-DVD Futurama movie involves our heroes contacting another universe, and then they encounter a planet-sized tentacle monster, voiced by David Cross. And Fry becomes pope of a new religion. (There are also planet-sized creautres in Tarkovsky's Solaris and in the GWAR mythos.( Here's the trailer.
Unicron from Transformers. We can only hope Michael Bay tries to take on this concept at some point — a mechanical planet who transforms into a humongous giant robot in space. And then he goes around eating other planets. In his first appearance, he was voiced by Orson Welles. I love how, in his planet form, he has giant metal horns sticking out. Party on, Unicron. But could he beat the planet-eating Galactus?
Gaea from John Varley's Titan. A planet-sized entity orbiting Saturn, Gaea is a "sentient space habitat that may or may not be batshit insane," as Bookslut puts it. The controlling intelligence of Gaea presents itself as a middle-aged woman who's obsessed with classic movies. In the second book of the Gaea trilogy, she offers miracle cures to humans whom she deems worthy, and in the third she provides a refuge for humans fleeing Earth's nuclear war.
Marvin The Paranoid Android, from The Hitchhiker's Guide To The Galaxy by Douglas Adams. Well, he's always reminding us his brain is the size of a planet, although we never actually see this mega-brain.
Solaris, The Tyrant Sun, from DC One Million. The "One Million" event, in which the Justice League traveled forward to the 853rd century to meet their curiously similar counterparts, was probably the 17th most demented thing Grant Morrison has written, and that's saying something. A giant artificial sun, Solaris causes his own creation in the late 20th century (thanks to a time-travel paradox) and then becomes one of Superman's arch-enemies. Finally, in the 500th century, Solaris becomes a good guy, but never quite gets over his jealousy of our solar system's "real" sun. So he plots to kill the original Superman, in a plot involving a galactic super-Olympics. To be honest, I've read this comic three times and still don't understand it.
Evil Nebula, from Captain Simian And The Space Monkeys. Half-human, half-black hole, Lord Nebula could run over Mogo and Ego and barely even notice. And the Evil Nebula thinks big — in the first episode, he decides he wants to absorb the entire universe into himself. ("It's an ego thing.") But he's not too big to come up with a monkey enemy for Captain Simian, the vicious Rhesus-2. Plus he's voiced by Michael Dorn, which is full of win.
The Behemothaurs from Iain M. Banks' Look To Windward (2000). Lev Grossman suggests these in his blog post. And StrangeHorizons describes them as "miles-long symboitic gasbags." They live in a massive drifting weightless
The Cloud, from The Black Cloud by Sir Fred Hoyle. In this classic 1957 novel, a Jupiter-sized interstellar cloud floats into our solar system and threatens all life on Earth. Scientists struggle to communicate with the Cloud — and they succeed. It turns out the Cloud has a "brain" made out of complex networks of molecules. And the Cloud turns out to be sort of size-ist towards poor limited humans:
[I]t is most unusual to find animals with technical skills inhabiting planets, which are in the nature of extreme outposts of life... Living on the surface of a solid body, you are exposed to a strong gravitational force. This greatly limits the size to which your animals can grow and hence limits the scope of your neurological activity.
Eventually the Cloud has a mishap and decides to leave our solar system, before we can learn from its ageless wisdom about the universe. But not before it's like "There was no Big Bang, kthxbai."
The spaceship-eating amoeba, from Star Trek, "The Immunity Syndrome." An 11,000 mile single-celled creature, this huge but pretty monster has to be destroyed before it reproduces and eats the entire galaxy. There's also an episode of the Trek animated series, "One Of Our Planets Is Missing," where they go inside a similar huge creature that's draining their power and munching on planets. But in that case, Spock manages to communicate with the creature, which is another one of those size-ist jumbo sentients and doesn't believe that such tiny creatures as ourselves could be intelligent. You could also make a case that the massive planet-crusher in "The Doomsday Weapon" is sentient, although it's never made clear. And another giant Trek baddie, of course, is the "crystalline entity" who stars in some of the most boring TNG episodes. Oh, and then there's V'Ger from The Motion Picture.
Jane from the Ender's Game saga by Orson Scott Card. An artificial intelligence, Jane occupies the entire galactic ansible network and is the only one who can make faster-than-light travel possible. Her one weakness is that when the Galactic Congress shuts down the galaxy-wide internet, she shuts down too.
The Calebans, from Frank Herbert's Dosadi Experiment and Whipping Star. Huge, unimaginably advanced creatures, the Calebans manifest themselves as stars in our universe. They give humans the secret of the "jump door," which allows you to teleport anywhere in space instantaneously. As Timothy O'Reilly writes:
[T]he Calebans are as close to infinite beings as he can imagine. Their visible embodiments are stars, and on a deeper level the Calebans are one gigantic consciousness that forms the topological matrix of the manifest universe. The jump-doors are simply an expression of their pervasive existence behind or apart from space.
The Calebans are super-advanced, but they have one weakness: they can't break a contract. Thus, one Caleban allows a psychotic human to torture it to death, which spells death for anyone who's ever used a jump-gate. Probably the best argument for contract-law reform ever. Despite this pitfall, the Calebans are the biggest and brilliantest life forms in scifi.