Ghost started out as a pretty typical Iron Man villain. He's an industrial saboteur that made his own powered armor which gives him the ability to make himself and other objects intangible, as well as gain access to and control computer systems near him. He also usually has weapons that fire concussive blasts or electricity, but he's primarily a stealth character and avoids using them as much as possible. As was typical in the era he was created, his origins were glossed over in favor of a simple "this is a bad guy doing bad things" story, but the thing is that, other than fighting Iron Man, he's basically a vigilante, except that he doesn't fight guys with superpowers. He fights corporations.
Now, admittedly, he often does it for money, but that seems as much of a bonus as anything. After all, the Punisher regularly steals from the criminals he kills, but he's not out there shooting drug dealers for the money; it just happens to be how he pays for his expenses. Ghost (we never learn his real name) has an axe to grind with modern corporate greed and, in particular, the military industrial complex. He's like that crazy conspiracy theorist who thinks that GE is building spy satellites to control you through the fillings in your teeth. Given the world he lives in, however, that's not actually crazy.
In the Marvel universe, you've got the military industrial complex building giant robots to kill their own citizens for being genetically different, experimenting on people to try to make super soldiers, and actively engaging in corporate espionage to steal technologies from one company to give them to other, less scrupulous ones. The Red Skull managed to get himself into a position of power in the United States government using the ridiculously obvious name Dell Rusk. Shapeshifting aliens have stolen and replaced major players in every field from government to corporate to superpowered heroes and villains. Tony Stark built a satellite that literally made everyone on Earth forget he was Iron Man. Ghost isn't crazy for believing that the powerful people, and in particular the corporations, are out to get him and the rest of humanity; he's arguably one of the few sane people in the Marvel universe when it comes to his beliefs.
Ghost is a really interesting and fairly underused character. He's usually cast as a villain, although he's also been used as an anti-hero in Thunderbolts and Dark Avengers, but none of that really seems correct. If you really take a step back and look at his actions, he's often more of a hero than the heroes he fights. In a lot of ways, he's like a superpowered version of Bradley Manning or Edward Snowden.