Who is Palamabron from The Complete Poetry and Prose of William Blake and what is their importance?

Palamabron is a fictional character, who plays an important part in the complete body of William Blake's writings. He is supplanted by Satan, who repeatedly endeavors to take over his duties. Satan is eventually granted his duties, but there are some very strange consequences, one of which is that the horses and the servants react differently to Satan than they did to Palamabron...... something that leads to a trial. In the end, Palamabron is blamed and forced to give up his post.