The most common characteristics shared by many serial killers are the killing and abuse of animals in childhood, fetishism, antisocialism, a high IQ (but including poor performance at school) and alcohol and/or substance abuse. The fictional character, Dexter Morgan, displayed serial murderous tendencies from a young age. He would kill neighborhood animals and was forced by his father to fake emotions and normality to fit in. Looks like Showtime nailed it with this one. One of the most famous serial killers, Ted Bundy, was notoriously known for being cold and ruthless. During interviews, he responded to questions about his victims by calling himself cold and explaining that he couldn't care less about his victims. The cannibalistic serial killer, Jeffrey Dahmer, started out killing dogs and leaving their heads on a stick for others to see before moving on to killing and eating people. These are just a few examples among many that demonstrate that commonality is what makes a serial killer a serial one