The Scarecrow is an alias of father Dr Gull and Laurann Gull who were pirates around Cornwall in England.
Dr Gull was a pirate who escaped hanging in Jamaica and returned to England and led a double life of respectful doctor by day and wrecking ships on the coast by night. Dr Gull is a ruthless man without mercy, is obviously smart and was a confident doctor to keep everyone fooled.
Laurann Gull is his daughter and was blinded by hate for her father being hanged. Not as ruthless and cold blooded as her father shown by deciding to frame Lord Charles Trelawney and the 12th Phantom instead of killing them which would have been easier. She is still tricky and an above average fighter in sword and gun.
There is a follow up adventure with the 13th Phantom that has yet to be told. It is indicated that her hatred could be due to being lonely. There could be a story of redemption.