Nicholas Brendon, an actor best known for his role as a loveable underdog sidekick on the hit television series “Buffy the Vampire Slayer,” has died. He was 54. Brendon’s family announced the death in a statement posted on his social media accounts Friday. They said he died in his sleep of natural causes, but did not say where or when it happened. Brandon played Xander Harris, a close friend of lead character Buffy, on the show that ran from 1997 to 2003. Brendon had also appeared on the TV show “Criminal Minds” and alongside Bradley Cooper in the Fox sitcom “Kitchen Confidential.”