Short version because the normal version probably can't fit in one post (There's a reason why he is the way he is):
Graduated top of his class at the Federation Navy Academy, named one of the best tacticians to leave the school. After 2 years of working with the FDU, he was recruited by the Black Eagles (G-FDU Black Ops division. Espionage, sabotage, and assassination).
Got captured on a big job, was locked up for about a month, with 0 human interaction.*
Went 'insane', but a special type of insane. He seems completely sane 99% of the time, but everything he does, he does without reason. Every single move he makes, every person he kills, SEEMS smart enough that he's completely mentally stable, but in reality, he kills because he can. Part of it is his hyper-intelligence, the other part is just plain crazy. Part of this crazy compelled him to do some f*cked up things, such as being intentionally captured by a Caldari battleship, cutting the power remotely, and then killing off each and every one of them, for no reason. For every person he killed, he sent a file to the Caldari State's database, telling them when, where, and how he murdered them. This file also included name, age, and where the soldier's family lived.
Is now a Gallente criminal. Separate from any other pirating groups, but twice as dangerous. Every person that's sent to assassinate him is held back. He's smart enough to manipulate even the most dangerous assassins, to point the gun at their own head, mostly by showing them what he sees, and what he knows.
*Now, to explain what ZERO human interaction means. If you were to go a month without ANY physical interaction (With anything but the ground and air around you), you wouldn't last 4 days. On the 4th day, your mind is begging, DEMANDING that you find some kind of human, or lifeform, or anything really, that will keep you company. On the 5th day, your mind is struggling to maintain sanity, even making fake relationships with inanimate objects to satisfy the need for any type of lifeform. On the 6th, your mind starts to create a universe. This is exactly what Art did. He wasn't in there for 6 days, he was in there for 30. Not only did he have time to start the creation of a world around him, he had enough time to complete one. In his version of sanity, the Federation sent him there to kill him. A suicide mission. The Federation is an evil political super-power, hiding itself behind the mask of freedom and justice. This is why he fights the Federation. To end their "tyranic" rule.
TL;DR, Don't f*ck with Art, because he's crazy enough to slit your throat without a thought.
What he looks like:
https://lh5.googleusercontent.com/-TGL2VyMTD-E/UnRGvsTKLqI/AAAAAAAAACk/rAq6sCY5PI8/Xavier%252520Sorraine%252520-%252520ProfileMy EVE alt is pretty much Art, pre-criminal status.