There is a lot of readily available information online regarding Ahab's character in Moby Dick. To get you started, he is often referred to as a monomaniac - a person obsessed with one idea, in this case, his relentless pursuit of Moby Dick. Read his physical description and you will see he is evil and intimidating. His sailors are petrified of him. He has a wild look, he stomps about the ship on his wooden leg, and everyone runs (if they can) when they hear him coming. He has no regard for his men and cares little about the danger he may be leading them into in pursuit of Moby Dick.
As to the second part of your questions. If people are unstable, they often have obsessive qualities when they are wronged. Mentally healthy people may be hurt, but they either confront the person and try to work things out, or move on. Ahab's obsession over catching up to and killing Moby Dick is madness. He defies every known logical fact (regarding weather, how far out of the way it will take the ship to catch up with Moby Dick, the fact that he is captain of a whaling vessel and should be fulfilling his contract to obtain whale products, etc.) in his obsession.
To state that all people who have been wronged have obsessive qualities would be an error. However, there is often a correlation in literature between the two. In the classic novel "Wuthering Heights" the story line is driven by Heathcliff's obsession with obtaining revenge against those who either harmed him or took his love away from him.
Captain Ahab identifies Moby Dick as the devil. He tries to express that he does not fear the devil. Ahab is a strong leader who is able to control his men. He presents himself as a man on a crusade. He justifies violence by his actions. He is fanatical in his obsession. He demands total power over everyone around him. He is angry with the need for revenge against the great white whale and will achieve it at all costs. Even when his men disappear after being tangled in the ropes, he will not seek help. His only drive is to conquer the whale.