Who is Doctor Dawson from The Woman in White and what is their importance?

Doctor Dawson is the physician summoned to Blackwater Park to treat Marian's typhus. He and Count Fosco argue about which type of medicine that should be used to treat Marian until Fosco drives him out. Later, after Sir Percival and the Foscos depart Blackwater Park, Doctor Dawson returns to care for Marian.