Patrick was a very disturbing individual who had a solipsistic view on the world and believes himself to be the only "real" being. He also displays marked traits of being a psychopath. He's shown to have a complete disregard for the boundaries of others and has sexually harassed female students on several occasions. He is known to often masturbate, which he sometimes does while torturing animals. There is also another scene where he masturbates Henry Bowers. His report cards showed him as being an apathetic student. He also keeps a pencil box of dead flies which he had killed with his plastic green ruler.
The novel stated that Patrick had a strange delusion in which he thinks that he is the only "real human being" in the world. This is part of the reason that he murdered his baby brother, whom he thought was somehow becoming "real". He came to realize that there are rules in the world and these rules must be followed, so he believed his strange behavior was simply breaking the rules and he must not be seen breaking them.
Possible Replacement (Avery)
At the age of five, Patrick had a baby brother named Avery Hockstetter. Although Patrick initially had no problems with his parents having kids, he was only worried about whether or not that new child would "replace him" and become a "real mortal" like himself. Patrick eventually became delusional to the point where he murdered his own baby brother. On one dark afternoon, Patrick snuck into Avery's room while the baby was still asleep. Patrick then smothered Avery to death with his pillow, being sexually thrilled as he did so. Later on that day when Patrick's mother had found Avery dead, he sat and watched television while his mother screamed during the entire process of Avery's body being removed. His father later saw the marks Patrick's wet boots had made on the floor and slammed the door so hard the frame split in a fit of rage after coming to a realization. He never questioned Patrick about it though.
The Bowers Gang
Sometime during the later years of his childhood (most likely beginning in 1955), Patrick would befriend his equally (if not surprisingly less) psychotic fellow school bully Henry Bowers and become part of his group of friends, The Bowers Gang. However due to his disturbing nature and generally low reputation (even by bully standards), Patrick was possibly not very well liked by the other gang members and was generally only occasionally seen with the rest of the group.
The Junkyard (Death)
(Novel only) On one hot summery day, Patrick, Henry, Victor and Belch were down at a local junkyard, lighting their own farts with Henry's lighter. After a while, Victor and Belch leave after a short and brief dispute with Henry. After the two leave, Patrick gives Henry a hand-job, and even boldly offers him oral sex, to which Henry replies by punching him in the mouth. Worried that Patrick might tell his friends about the incident, Henry blackmails Patrick, threatening to tell the police about his "secret fridge" down at the Junkyard. After Henry leaves, Patrick heads down to the fridge to dispose the dead animals he kept in there, only to be attacked by flying leeches (his worst fear). The parasites drink most of his blood and eventually drag away his unconscious body. By the time Patrick had awoken, It had already begun feeding on him.
While under Derry, The Loser's encounter Patrick's decomposing corpse.