Exact details about Wilson Fisk's life are unknown, other than he has been a criminal since at least the age of twelve, when he committed his first murder. A fat, unpopular boy, he was often bullied in school. He eventually learned to use his size to his advantage. Fisk trained in martial arts and changed his flabby body into a mass of pure muscle, intimidating the other thugs in his tough Bronx neighborhood. His pure cruelty caught the attention of Don Rigoletto, a mob boss who hired Wilson into his gang. Later, Fisk killed Rigoletto and took over his portion of the mob.
While not formally educated, Wilson did teach himself political science, which he made use of while running the mob. He also rose to power shortly after Spider-Man removed the mob leaders, Crime Master and Big Man, from the scene. This power vacuum aided the Kingpin's power grabs. "Instead of many rival gangs operating haphazardly throughout the city, instead of countless crooks acting alone...the underworld will now be run like a business. And the chairman of the board will be the Kingpin!" (Amazing Spider-Man #50)
Fisk and Spider-Man clashed numerous times over the years, sometimes physically but more often in a sort of cloak and dagger way. Kingpin's tendency to actually take part in his crimes gave way to having underlings and unwitting dupes do his dirty work. He has used other criminals (from the Hobgoblin to Jack O'Lantern) and vigilantes (Daredevil to Spider-Man) as pawns in his schemes. An intimidating bear of a man, Fisk's physical strength is not to be underestimated. His strength is not superhuman but is more than enough to kill an average human with one punch.
Psychopathology: Narcissism and Cyclothymia
As the Kingpin's criminal empire expanded, so did his ego. Always the audacious type, one of Wilson's first acts as Kingpin was to kidnap newspaper publisher J. Jonah Jameson to silence him and his anti-organized crime campaign. Spider-Man was also captured and sent to drown with the publisher in a sub basement. As Jameson pleaded for his life, Fisk snorted "You fool! The Kingpin can do anything!" (Amazing Spider-Man #52)
Spider-Man knows about Kingpin's narcissism. After Peter unmasked to the public as part of the Superhuman Registration Act, Fisk hired a sniper to kill Peter's beloved Aunt May. Filled with rage as his aunt lay in a coma in a hospital, Peter confronted Fisk in prison and beat him in front of the assembly. As Kingpin lay bleeding on the concrete, Peter let him know how it was going to be. "You see, I've learned something from you, Fisk. Something about cruelty...and timing. I've done something far worse than kill you, Fisk. I've beaten you...And for a man as prideful as you, who needs everyone to believe he cant be beaten...that's the worst pain you can feel." (Amazing Spider-Man #542)
Cyclothymia is characterized by a milder form of mania and depression. Fisk would go between states of high moods and depression, but these episodes would be milder than full blown manic depression. For example, look at the differences of emotion when Kingpin says "At last! With Spider-Man gone, the city is mine!" (Amazing Spider-Man #51) and his dreary outlook when Spider-Man faces him after a gang war. "Spider-Man, I've made several fortunes via the practice of using people like you...Trusting idiots that believe there is happiness to be had on this planet." Even the threat of death doesn't stir him. "My death would serve no purpose, other than to bloody the hands of such God fearing men as yourself." (Amazing Spider-Man #288) It should be noted that Fisk's wife, Vanessa, was forced to flee to Europe during the gang war, possibly explaining Kingpin's depression.
The Kingpin of Crime: Family Man
Despite being willing to kill anyone if it means protecting his empire, Fisk is a devout family man. He fawns over his wife, and was a proud father to Richard. Richard had believed his father to be an importer of Asian spices, but was devastated to learn that he was a mob leader. The news that his lavish lifestyle was paid for with blood money made him hate his father. He faked his death, causing Wilson to fall into a deep depression. Richard later planned to take apart the Kingpin's empire as the Schemer, and his unmasking shocked Wilson into a catatonic state. They eventually reconciled, despite other sabotages by Richard. Rich was eventually killed by Vanessa after a final assassination attempt. This father/son struggle for power and redemption is similar to another New York crime family: John Gotti Senior and John Jr.
Wilson Fisk is hugely full of himself. It may seem to be with good reason, until you dig deeper. While he is an extremely healthy specimen, he throws himself against super humans and expects to win. Kingpin does put up a good fight but his narcissism cost him dearly when faced against an irate Spider-Man. Fisk has gained control of the mob numerous times, but only after losing it to other gangsters and super criminals. He is a force to be reckoned with but is not the force of nature that he thinks himself to be. Kingpin is also not mentally ill. His murders are goal oriented, not committed out of blood lust. This puts him low on the psychopathic scale.