Friday is skinny and pale, his eyes are purplish, his hair is gray and he mostly wears a white shirt along with black pants. Being a corpse, his looks are emotionless and soulless. He obeys Watson and doesn't speak.
The reason for his name, Friday, comes from the fact that he was a genius who would always spend his Fridays at the grand library studying.
When Watson found the Notes, Friday's soul was being brought back to him, he whined and screamed, trying to speak. When he loses control he attacks Watson and tries eating any human in the way.