Summary for the lazy people: Descartes is a 16 years old mewtwo, standing at 4' 8". He has a black belt with a device on it, that is a computer, an holographic projector and an AI. He can be rude and thinks highly of himself, but is friendly if you can go past it.
Mistress: He is now a slave to _Renamon_. Poor boy.
The real stuff
Backstory
"They say Arceus created all that there is. That's moronic, because only a psychopath could have conceived this gate. Then again..." -- Descartes, before Gate traveling
"Gate's power: 90% All personal prepare for transportation." boomed a computer voice around the large chamber, a fact Descartes had hoped to forget. Travel through David's Gate had never been a pleasant experience, even for him. Many had lost their sanity by making the single mistake of opening their eyes during the trip through the bowels of the Void, a realm the Exarchs ruled with an icy grip. The pokemon had done that mistake himself once, way back when he had still been a little kid. The images of mutilated dark creatures of impossible shapes and horrible proportions were still imprinted deep in his brain, leaving a scar that never truly healed, the cause of his deep hatred and fear of this mode of transportation.
Unfortunately, it was the only method currently available to explore the universe past their own galaxy. The David's Gate, named in honor of the man who had discovered it, was a technological wonder that still baffled the scientific community. Standing at ten feet tall, it was an arc made of an unknown metallic alloy, decorated by carvings of the First Borns, or more exactly, their ancestors. When powered by an intense input of energy, the gate would flicker and open a wormhole between two points in the universe, always two gates of the same origin. Current knowledge bases acknowledged the existence of 14 Gates, but the existence of more Gates was uncontested, all that was needed was to find the coordinates of a new one using the rather confusing device attached to the Gate.
"Gate power: 100%. Gate opening. Please close your eyes or wear the authorized protection equipment during the opening procedure. Failure to do so may incur a risk for your health. Irongate Corporation cannot be held accountable for any damage caused by a failure to obey this directive."
The teenager repeated the monotonous warning in his head in boredom and annoyance, his three fingers tapping onto his belt. He had been chosen by the army for this exploration mission, sponsored by his father, the first Mewtwo. He had initially rejected the idea, but after yet another argument with his mother about his own safety, he figured that he could use a break from it all while pissing his mother off. As an honorary member of the First Born, the highest division in the planetary army, the teenager was granted the finest of equipment, a black computerized belt housing a portable quantum computer and a state-of-the-art solid-state holographic projector. It was mandatory, as per protocol, that he wore his uniform around any military installation. A fact that he found to be rather ridiculous, given the fact there was only two Mewtwo in existence and thus pretty much everyone knew who he was without the need for any identification.
Much to his relief, active electronic equipment wasn't allowed during the trip, as it could damage it, 'forcing' him to turn off the holographic suit before he stepped through the Gate, enveloped in a cold feeling of death and sorrow characteristic of Void travel. It only lasted a few seconds... or that's what it usually did. Seconds passed, becoming minutes, without the end within the reach of his senses. Annoyed and anxious, the feline pokemon opened his eyes, immediately assaulted by the dark forces of the Void. Scared, lost and confused, the teen launched a powerful blast of void energy, shearing through its fabric with amazing strength. The energy rebound caused by such a reckless action weakened the young pokemon, knocking him out.
He woke up minutes, hours or days later, he couldn't tell anymore. He opened his eyes to the sight of a vibrant green field in a sunny weather. The feline sat up slowly, taking a glance at his new surroundings. "Am I... dead?" he asked to himself, but the presence of his belt reminded him of what he had been doing and what had happened. He had gone through the Gate and then... he had landed here, in this field. He immediately figured out that something had gone horribly wrong. No planet linked to a Gate was luxuriant, other than his home world and even then, the Gate was deep underground. Most critically, something felt wrong with the universal laws. Getting back to his feet required almost no energy, and a quick scan through his known abilities revealed that there was much more looseness in the rules of their pratical application. Wherever he was, this wasn't Mt. Moon anymore. It wasn't his galaxy, it likely wasn't even his own universe. With no Gate in sight, the mewtwo reactivated his uniform and started looking for a way back home...
Past
"Your upbringing doesn't determine who you are, but it sure as hell determine who you have to deal with. No mom, I'm not going to hurt myself with the laser gun!" -- Descartes, during target practice
Descartes was born about 100 years after the 'present' in the pokemon world and 20 years after the Soulphage war, where entities of the void invaded the world and tried to destroy all life, forcing the all the First Borns (aka mew), humans and pokemon to work together for the first time in history. War had brought great progress and technology, pushing the limit of the human and pokemon bodies. In this context of growth, a mew named Miya had rebelled against the current rigid mew institution and got together with Mewtwo, the symbol of everything the mew authorities did not believe in. Des was born out of this relationship, made in vitro like his father.
Des had a pampered childhood, with his father teaching him classical music, the art of fighting and other fine arts, while his mother showered him in love, both preaching the belief than Mewtwo were genetically superior to everything there ever was. As he reached his teenage age, Des grew more distant with his mother, her obsessive love becoming more of an hindrance than anything else. At the age of sixteen, he became a cadet in the Planetary army, under the First Born Alliance, granting him immediate respect despite his low rank. He was sent on an exploration mission through the David's Gate when something went wrong...
Physical apparence
"Hey, I'm not small, I'm just not fully grown yet. You dare call me small again and I blow your head off!" --Descartes, arguing with a human soldier about his height
Descartes looks like your regular mewtwo, but since he is only 16 year old and has mix of mew and mewtwo DNA, he is only 4 feet 8 inches. His features, as shown in the profile picture, are slightly more roundish and childish than a full grown mewtwo, but don't be lured into a fake feeling of safety. While he isn't as powerful as his father yet, he is very powerful, and even more so now that he is in this dimension. He wears a black metallic belt, which will be explained in further detail in the next section.
When the solid uniform hologram is active, he wears two shoulder pads, proudly displaying the planet-shaped logo of the army. He also wears a light, black protective jacket, which double as a mean to display his name, his grade and his association with the First Born, in the shape of insignias over near his heart. If the device is not in use, he looks like he only wears the belt.
Holographic belt
"This kind of technology is a double-edged sword. On one side, it comes with nice holographic projector, a computer to listen to my classical music and a S.A.M. A.I. equipped with a First Born Data Matrix... on the other side, it comes with a S.A.M. A.I. equipped with a First Born Data Matrix. Darn, these things are almost as annoying as my mom is. Where's the off button on this thing? I demand an off button!" --Descartes, while testing the belt
The belt Des is wearing is a gem of modern technology. As described in this quote, it is equipped with three main devices, all subtly integrated in a streamlined belt, with only one button to turn it off. The everything else is controlled mentally.
-The solid-state holographic projector: Since the invention of the Mirage pokemon, the art of creating solid objects made out of a mix of light and force fields had been refined to allow the creation of up to ten objects at once onto a portable belt. Pretty much anything that isn't heavier than a ton can be materialized by the projector, allowing for a great deal of versatility... at least when humans are using it. The Mewtwo deems himself too powerful to lower himself to use that thing and rarely does it other than to generate his uniform. He will use it upon request, though.
-The portable computer: The computer system has is a portable unit running on a quantic 20Ghz processor, with 2 Tb of RAM and a 'drive' of 20Pb of memory space (although most of it is used to hold the First Born Data Matrix). This computer contains all of Des' music, videos, and other important data. It also has some games. The computer has a few ports on his belt for backward compatibility with older technology.
-The S.A.M. A.I. unit, coupled with First Born Data Matrix: The unit, nicknamed Pi, is Des' official partner in science, and Des hates her. The A.I. has a soul of her own and can be materialized using the projector, in the form of an 18 year old blonde-haired woman. Very kind and technical, this virtual assistant is equipped with the First born Data Matrix, which is the compendium of all mew knowledge, effectively giving the A.I. advanced mind and intelligence. Pi can help Des with a large quantity of task, as she can faintly affect the world around her. Most of the time though, Des keeps her locked in the computer, because he doesn't like to be ordered around, or given advice. In fact, he hates it.
Personality
"I'm a kind person. Really, there's no one more kind than me here. Or powerful. Or awesome. I AM the most powerful pokemon in the world after all." --Descartes, bragging as usual
Pompous would be a good summary of who Descartes is, since he was raised to think of himself as better than anyone else. It does often get him into trouble, trouble that he tends to solve using brute force and his signature move, the Void Ball. Part of his attitude is attributed to his rebellious teen age, which also comes with sexual moods. While he isn't outwardly sexual, he may do a few remarks here and there when the mood strikes him.
Under that tough shell, lies a somewhat fragile individual who hates his mother and his AI, but who learn for the love of someone. He can be gentle when he isn't in his militaristic mood and he is surprisingly dignified for a creature built on pure power.