If books are like our children, so are the characters in them, and it seems like there's always one in my stories who needs attention. He demands that he become more than I intended him to be. A guy I needed for just one turn in the plot won't leave after his hour on the stage has been strutted and fretted away. In MACBETH'S NIECE it was Banaugh, who started out as Tessa's escort to Macbeth's castle and ended up staying through the whole book, providing all kinds of help for her and finding happiness for himself along the way.
In my WIP, it's a baddie. Meant to be a temporary threat, he's become a sort of mirror image for the #1 baddie: where one is misguided, the other is knowing; where the protagonists might escape one by laying low, they can't escape the other, who is relentless.
It's just another example of what authors say all the time: characters make their own way in a story. You can't make them be quiet if they don't want to, and you have to allow them to be what they are, or there's a gap that readers notice. "What happened to the mean guy?" I can hear them asking. "He wouldn't just give up and go away. He's the kind that holds a grudge."
So he will stay on, even if it means going back to the beginning and giving him a bit more depth in Chapter One. Heaven forbid I should deny my children the attention that's due them.