Julie Hertzog said it once was thought that defining a bully was simple, and potential bullies were easy to spot. Think of the movie, “A Christmas Story,” she said, and the bully named Farkus.

Hertzog, the director of the Pacer National Bullying Prevention Center, said it’s now evident it’s not that easy. Casting the bully as a physically intimidating outcast isn’t necessarily accurate, she said.

“There is no particular profile,” she said. “It used to be that people thought that kids who bullied had very low self-esteem, but we’ve found just the opposite to be true. A lot of times they are social leaders.”