Who is Eugene Haas from The Magician's Assistant and what is their importance?

Eugene Haas is Bertie's long time fiancé. He is described as a quiet schoolteacher, who truly loves his intended wife. who dotes on his future wife. He is calm and unobtrusive........ at least until Bertie is hurt by Howard Plate's actions. He then makes it very clear that no one messes with Bertie.