A mysterious individual that sells information and likes to put individuals in awkward situations in order to observe their reactions.
A young man who sells information for his own enjoyment. He claims to love the entire human race except for Shizuo Heiwajima, and exhibits said 'love' by putting humans in often miserable conditions and observing their reactions.
He once attended Raira Academy with Shizuo, Shinra and Kadota. According to Shinra, Izaya and Shizuo hated each other with a passion almost from the moment they met. In the novels, Izaya actually framed Shizuo for crimes in several occasions while in the anime he purposely causes problems for him, from sending gangs to attack him daily to framing him of crimes.
He is a master of parkour, and quite skilled with his flickblade (the blade he uses must be slightly opened before the mechanics of it springs opens the blade - a switchblade will open on its own after the user presses a switch) as it is implied he was the only one capable of leaving numerous cuts in Shizuo's bartender suit after a fight in the novels. In the anime, he shaves a gang member's head bald without him noticing it. He is also part of the anonymous online gang: Dollars. He is usually seen pretending to be female online and talks in a feminine manner in the chatroom under the screename "Kanra". Notably, Izaya has two younger sisters, Mairu and Kururi, who are twins and troublemakers, who both seem to have a crush on Shizuo's younger brother Kasuka.
Later on it is found out that he is the main antagonist. His name comes from a combination of the biblical Isaiah and Japanese for "the one who looks over the crowd".