A topic, idea, or agenda that is a source of obsessive fixation or preoccupation for one. Sometimes written "King Charles' head" (with no "s" after the apostrophe). An allusion to Charles Dickens' book David Copperfield, in which the character Mr. Dick is unable to write or speak without bringing up the topic of the severed head of King Charles. Immigration reform, the King Charles's head of the party in recent years, was again the focus of today's debate. My poor aunt can't help bringing up her troubled childhood whenever she begins a conversation with someone. The trauma of it all has become a kind of King Charles' head for her.