Henry Miller is a rouge element in DSaF2, he is described by Dave Miller as "devil incarnate".
Although he does not make a physical appearance in Dsaf2 he is mentioned rather regularly.
This character is pretty vague however most of the story is pieced together.
Henry used to work alongside William Afton (Dave Miller) back at Fredbear's Family Diner. William would kill kids at Fredbears and Henry would kill kids at Freddys so that Freddy's could never overtake them. However the Fazbear company bought out Fredbears and the Fredbear character. He even killed Peter (Human Phone Guy) By triggering the springlocks in the suit.
Henry is also responsible for the Freddy blowtorch urinal incident and the death of the main protagonist Old Sport.