Who is Mr. Jenkins?

A Wind in the Door is the second book in The Time Quintet, a series by Madeleine L'Engle. The first book in the series is the renowned A Wrinkle in Time.
Mr. Jenkins is the principal at the school that Charles Wallace attends, and he is a returning character from A Wrinkle in Time. When Meg finds out that Charles Wallace is being bullied by other children at school, she tries to ask Mr. Jenkins for help, despite having had her own issues with Mr. Jenkins in the past. Unfortunately, she ends up being disappointed when he refuses to give any help regarding Charles Wallace.
Later on, as Meg, Charles Wallace, and Calvin are beginning to fight against the Ecthroi, Meg is put to the test when she must distinguish the real Mr. Jenkins from two evil Ecthroi body doubles.