I decided to leave this thread open to great characters and the links between their design and stories, but what I really want to do is talk a bit about how excellently designed some creatures are and then hope that all of you do the same.
In my mind, the aliens from the.. Alien.. films are one of the greatest creature designs ever. I saw the recent Alien v. Predator and that was one of the greatest draws for me. I'm not only talking about their appearance, either. When I was younger, I rented Alien 3 for SNES. The manual contained a lengthy description of the alien lifecycle that totally fascinated me -- so much so that I copied the whole thing by hand into my Trapper Keeper.
Another memory I have from years past is drawing metroids. A lot. I've taken to doing it again, too, because the newer games since Fusion have reminded me how much I love them. As far as alien creatures go, their design could not be more direct; they seem like the quintessential creature in some ways. They have a hemispherical, transparant shell, and inside this four main nerve clusters and a network of shoots are visible. At the bottom edge of the shell, the nerve branches culminate in four large teeth-like claws. The metroid feeds by trapping its victim under the open part of its shell, holding it with the claws, and directly sapping its energy.
Of course, this direct energy feeding bit has been the driving mystery of the metroids, and the early games made it clear that it was the reason that the metroids were of such great interest to Federation scientists and Space Pirates alike. The latter discovered that, when exposed to high levels of beta radiation, metroids asexually reproduced by splitting. The Pirates also exposed metroids to other radioactive elements such as phazon to cause them to mutate and grow to great size, controlling the specimens through their weakness to cold with the intent of using them as biological weapons.
The story of Super Metroid brilliantly and elegantly fuses this backstory, which is basically from the first Metroid game, with that from Metroid 2 to create a tragedy that Samus experiences in Metroid 3's Tourian. In Metroid 2, as Samus, you defeat the Queen Metroid and climb towards the planet's surface. On the way, you come across an egg that hatches when you approach it. A tiny metroid emerges, quizzically squees at you as you level your gun at it, and then begins to encircle you. The in-game event effectively conveys that it considers you to be its mother. After a moment's hesitation, you continue to the surface, and it follows you. The back-story between the games tells us that Samus placed the hatchling in the care of Federation scientists for study -- perhaps the power of the metroids is not only a danger to the galaxy, but can be harnassed for good.
In Super Metroid (Metroid 3), the Space Pirates return, kill the Federation scientists, and steal the hatchling. Samus follows Ridley to Zebes, where they have rebuilt their base and laboratories, to retrieve the hatchling that she spared on SR388. At the end of the game, you draw near to the center of Mother Brain's lair, Tourian, and begin to see strange sights: creatures like those that you have fought throughout your descent into the planet's depths lie dormant in this place, their bodies the color of sand. When you approach them or fire at them, they simply crumble away to dust. Soon after, you discover the reason, as you witness a large one caught and devoured by an enormous metroid, far larger than any you have seen. After the creature is drained of energy, it spots you. You try to escape, but it is too fast and plants itself on you, draining your energy tanks until you are almost lost. Suddenly it stops and gently releases you, making soft squeeing sounds in recognition, for this is the very same metroid as that hatchling from SR388. You are shocked by the change; the Pirates have turned it into a monster. It flies away, as if in guilt, and you find a station where you replenish your energy before continuing to the heart of Tourian.
There you battle Mother Brain, as you did in the original Metroid game. This time, however, she reveals her true power. After an epic battle, your weapons ultimately prove too weak, and she pins you, disabling you and draining your energy with a laser attack. At the last moment, the giant mutated hatchling swoops in and plants itself on her monstrous head; she frantically stomps back and forth, shaking her head with violence, but she cannot escape its grasp. It drains her energy as she kneels to the floor and turns a dormant gray. The giant hatchling then reveals an unknown ability as it plants itself on you, Samus, and restores your strength, reversing its naturally ability to drain energy in order to save your life. Behind it, however, Mother Brain begins again to foam at the mouth, her color returns, and she rises to her feet. She attacks the metroid as it remains covering you, protecting you, and before long it can take no more, lets out its final squee, and crumbles before you. Suddenly, you stand up, and you are more powerful than ever before. You fire at Mother Brain again and again with a new beam weapon that is powerful enough to make her recoil and scream at each blow. Finally she falls, and her body turns to a familiar sand-like color. You fire one last time, and she crumbles into dust at last.
Did the metroid imbue you with the power that Mother Brain had used to attack you? Possibly -- your new beam has the same rainbow flash as her draining weapon. But maybe you somehow gained the power of the metroid itself, since she turned to sand like its victims had. There is also a clear element of rage in Samus, and the player can tell that this has empowered her, besides what other transfer may have taken place.
I love metroids. Like the aliens of Alien 3, I took the time to think about them biologically. I wondered about the effects of radiation upon their bodies. I relished every bit of theoretical information about their energy draining abilities and neural clusters that I found in the Space Pirate logs of Metroid Prime. I thought about their lifecycle, from the underdeveloped jelly fish-like mochtroids found in Maridia to the adults of Tourian to the shell-shedding, mutating alpha, gamma, zeta, omega, and queen forms of Metroid 2.
The Metroid series, uniquely, can be said to be about Samus, but just as definitely it is about the metroids. It is the story of a an unusual species with strange power that different groups seek to harness. It becomes the story of Samus and one metroid in particular. The entire thing is so elegant and enticing that it infuses the Metroid games with something intangibly wonderful that they would never have had without it.
So do you have a creature or character design that you find very interesting or that does wonders for a game?