Virus 138 is usually depicted as either a computer virus or a hacker. His personality varies. He can be characterized as clinically insane and wild. Or sadistic and murderous in intent, which would make him even more cut-throat than Izaya. Some people will portray him as a hacker in the real world who has an unnatural obsession for finding information (even more so than the info-broker, Izaya) and will go to any means to obtain what he wants. When he has an objective in mind, he will manipulate and stop at nothing to obtain it. Sometimes he is seen as a bit hyperactive and almost foolish, but those characteristics are normally just on the surface as opposed to his deeper personality traits. What lies underneath is normally a mastermind, or as said before, a mentally unstable person. It depends on how dark you think he truly is.
Virus 138 has red eyes and sharp, pointy teeth. He wears a typical, white dress shirt and a black vest. In fanart, the vest varies in different ways. Sometimes it's short and only has two red buttons, and other times it's long and doesn't have any buttons. Sometimes he wears typical black dress shoes, and other times he's shone wearing black and/or red boots. One of his more distinct dress features is the red ribbon around his neck. It is either tied up in a bow or like a loose-fitting neck scarf. He is usually shone wearing short, black gloves, and he's always wearing black and red headphones. He is sometimes also shown holding one or two handguns.