Cooper Davis Burtonburger is not actually a human being. He and Kat are Siamese twins, born conjoined to the back of their heads before they were surgically removed from each other. That's why their heads look different from the other characters from the show.
Kat's mother was pregnant with two kittens, but she noticed that her kittens were born conjoined. She also noticed that there was a good twin, and a bad twin, and she couldn't risk having an "Evil" twin, so she had to give one up. She chose to keep Kat, thinking that Kat was the good twin, not realizing that, unfortunately, he's actually the bad twin. The commander's soldiers abducted a woman in the 70's and implanted the good twin inside the woman's stomach and took her back home and flew away, leaving her to think what just happened. One day, she became pregnant with Coop, who has morphed into a human being due to the umbilical cord and the amount of blood cells inside the woman. She then gives birth to him, and because of family matters, she left the man who reveals himself to be Burt Burtonburger, who was an alcoholic before he went to rehab.
The reason Kat and Coop always bicker and fight is because Kat was jealous of Coop having the spotlight back on earth, while he does nothing but cause trouble like the bad twin he is. Until, he got an idea to turn the tables; Kat would be the good twin while Coop gets to be the bad twin.
Even though Coop doesn't have his cybernetic, hairless skin, he still does have three natural hearts, one mechanical stomach (which explains why he can eat so much), two motherboards connected to two brains, and a mechanical left eye (unknown whether both of his eyes are mechanical or not), but he hasn't learned to perform his powers yet because of the abortion. There was no other alien cat to teach him how to do his powers, and no one to contact, he became lost in the human world, not knowing that he is actually a highly-evolved Sphynx cat. But he does have the same healing factor, which he didn't notice.
Burt and everyone in Bootsville doesn't believe that Kat is an alien, and defiantly not know that Coop was one as well. If they knew that, they would immediately freak.
Now and days, Coop likes to spend his free time with his skateboard. He is also into skateboarding, soccer, and just hanging out with his friends (particularly Dennis, Lorne, Harley and Fiona). All of this changes when he is then forced to try to defend Earth from Kat's schemes. Coop attends school with Dennis and is a capable student with grades that tend to both rise and fall depending on the obvious situations at home. He does try to study and finish his homework quickly due to having to fend off Kat and avoid getting into trouble. Coop's life at home usually involves a confrontation with Millie or Kat. This lead to the construction of a Tree-Fort in the backyard, in order for Coop to put some distance between them. Though there are times where everyone can appear to get along, such moments of peace are typically short lived.
Coop and Burt get along very well, as they have a strong relationship based on similar interests and Burt's own understanding of what life as an 11 year old boy is like. Coop is shown to care deeply for his (adopted) dad and has followed his directions almost every time.
Coop's younger sister Millie regards her brother as somewhat of a nuisance, blaming him for anything and everything she can. While there are moments the two siblings can get along, they are few and far between. Millie thinks that Kat is the important part of the family due to the fact Kat is supposed to be cared by the whole family.
Dennis is one of his few allies against the combined forces of Kat, Millie and Old Lady Munson. Like Coop, Dennis also knows Kat's true identity, and together he and Coop try their best to foil the alien's "evil schemes". Since they were young, Coop and Dennis have done everything together, they enjoy the same hobbies and interests and are both big fans of Captain Blasteroid.
Coop has had a crush on Fiona since they first met, and it seems that she has a crush on him as well, seeing as she admits her liking for Coop.
Coop probably does not like Aunt Beatrix. Her trailer creeps him out, she seems a bit odd to him and, based on his reactions, he seems to have been at her place a lot.
Coop doesn't like Kat's Girlfriend that much because he doesn't trust her (due to the fact that she doesn't see him as the good twin because of she thinks that Kat's the good twin since the twins' birth). She also helped Coop and his friends escape from Kat Nebula.
Despite the many hardships with Kat, he sometimes (rarely) cares for Kat, and would actually think Kat was a cute little kitty if he didn't know Kat was really an alien. If that's the case, then maybe they knew that both characters are twin brothers all along and still has that brotherly love with him. Maybe I'm second guessing myself, I genuinely don't have a clue.
And one of these days, Coop will finally know the truth, and the question remains; how will they react if they finally saw that Coop was the Soulless feline boogey-cat that he was? But, most of all, how will Coop react? Would he react badly, or be thankful that there was some purpose behind it?
Those questions today, remains a mystery.