Janith Samarasinghe was Ambrose de Ripariis' loyal gentleman's gentleman.
Ambrose brought Janith to England in the 1870s when both men felt a preternatural familiarity. Janith is never treated as a servant, but as a trusted friend, and it always remained that way.
Before Janith met Ambrose, he didn't believe in magic, deeming it a mere escape from the hardships of life. Since they became friends, however, Janith thought the power of magic was the one reality on this planet.
Janith had an impoverished childhood, but never lost his inner light. He believed his early suffering was what made him strong. Janith is a enigmatic character throughout the quartet but his role is well understood by the end.