Scarecrow was once a professor at Gotham University named Dr. Jonathan Crane. Due to terrifying childhood trauma that left him mentally unstable, Crane became obsessed with the emotion of fear. When his cruel experiments on others were deemed too dangerous, Crane was fired. To exact his revenge, he became Scarecrow, making the citizens of Gotham City his test subjects.
Credits to @alexissosa for the synopsis
P.S., THIS IS NOT A REEVESVERSE FILM.
