<human>:  Why did Dexter kill his sister in the TV show ‘Dexter (TV series)’?
<bot>: Dexter is a serial killer. He kills people because he is a sociopath. Sociopaths are people who lack a sense of empathy for other people, and they often have no conscience or remorse. Sociopaths are usually quite charming, and they often appear to be very normal. Sociopaths are often very intelligent and very successful, but they are unable to feel any emotions that others feel.