Dr James Mortimer – A medical practitioner and friend of the Baskervilles. Mortimer is tall, thin, and good-natured with rather eccentric habits. He is, nonetheless, a competent country doctor who was made the executor of Sir Charles's will. He sets the book's plot in train by travelling to London to inform Holmes and Watson about the strange events surrounding Sir Charles's demise, and alerting them to the dangerous situation that Sir Henry now faces as Sir Charles's heir. Mortimer continues to assist Holmes and Watson in their twin roles as investigators and bodyguards until the conclusion of the case.