Kim Namjoon was only 8 years old when he was admitted into the asylum due strange behavior and pets going missing. He didn't last long though, thanks to brutally stabbing another patient for trying to steal a nurse he had been flirting with. They then threw him into a padded cell and observed him for 5 years, not allowing him to leave. Once those 5 years ended, however, he was finally diagnosed with Multiple Personality Disorder. Thanks to finally discovering this, he was then brought back to the asylum where all of the doctors and nurses were then warned of him and his personalities.

Kim Namjoon has 5 personalities to this day:

 

Namjoon is his regular self. Curious and sweet, but quite calm and wouldn't hurt a fly. Namjoon will naturally love anything as long as it doesn't hurt him or others around him.

Rap Monster (RapMon) is the personality that naturally doesn't give a about anything. The only real thing he truely cares for is his music and satisfying his fans at the asylum.

Skyler is the ual predator of the bunch. He won't stop till he's found something tight enough for his to fit in.

Max is the violent possesive one. He'll do whatever he can to satisfy his hunger for blood and screams. He's the personality that came out when he stabbed that other patient. If you touch anything/anyone of his, he will literally kill you.

Alex is the personality of his that you will never want to meet. It's the most violent, possesive, and addicted personality you ever could meet and is one that you want to avoid at all costs. Alex will only really come out if any of the personalities feel slightly threatened. Either or, you never want him to come out. If he sees you trying to take someone of his belonging, he'll find the worst ways imaginable to torture you till you wish that you were dead.