The source of inspiration Kane found for the character came from Washington Irving's The Legend of Sleepy Hollow whose main character, Ichabod Crane, also had an odd scarecrow-like physique.
As a young child, Jonathan Crane was subjected to sick and twisted experiments on fear conducted by his own father. Emotionally scarred and mentally unstable from the ordeal, Crane spent his childhood living in fear until he made an important realization—if he could control fear, it would never again control him.
Dr. Jonathan Crane was a psychiatrist at Arkham Asylum who conducted experiments on inmates under the identity of Scarecrow. He was portrayed in the Batman Nolan Film Trilogy by Cillian Murphy.
In his first appearance in World's Finest Comics #3 during the Golden Age of Comic Books, the Scarecrow is first introduced as Jonathan Crane, a professor of psychology, who turns to crime after he is fired; an expert in the psychology of fear, he had fired a gun in a classroom full of students to illustrate a point.
Batman then grabs Scarecrow's vial of fear gas, crushing it along with the supervillain's hand, and cuts Scarecrow's head off with his own sickle, declaring that Scarecrow has no idea what fear really is.
After being mauled by Killer Croc, causing him to wear a leg brace and surgically reconstruct his disfigured face to resemble his mask, Scarecrow forces the civilian evacuation of Gotham by threatening to unleash his new, more potent strain of fear toxin on Halloween, allowing the Knight's militia to occupy the city.
They're all fairly twisted, completely devoid of any hope. But on one world where the Scarecrow's fear toxin has become a permanent part of the atmosphere, it is revealed that John Henry Irons, aka Steel, is immune to the effects of the fear toxin, something that not even Batman can lay claim to.
Speaking to Rolling Stone, Nolan confirmed that the mask dispenses an anesthetic that keeps Bane's pain controlled, and the flashback sequence explains the need for this, as the attack in the Pit left him with serious injuries.
The psychopathology Arthur exhibits is unclear, preventing diagnosis of psychotic disorder or schizophrenia; the unusual combination of symptoms suggests a complex mix of features of certain personality traits, namely psychopathy and narcissism (he meets DSM-5 criteria for narcissistic personality disorder).
Through her aggression, deceitfulness, theft, and serious violation of rules, Selina displays traits of conduct disorder, the childhood precursor to antisocial personality disorder.
If Wayne actually believed that he was a bat (that is, if he had delusions), it would certainly suggest a mental illness such as schizophrenia or delusional disorder.
Weakness: Scarecrow's weakness is his anxiety disorder. He is also addicted to and obsessed with fear, including a fear of bats and a fear of crows after being attacked at his family's aviary.
Jonathan Crane is a doctor and was also a professor of psychology before getting fired, which was the catalyst for him turning into Scarecrow. He decided he'd embrace the nickname he'd gotten for being scrawny and wearing shabby clothes by becoming a symbol of 'poverty and fear'.
He has a white father, and a Latina mother. But as someone who never knew his father until he was an adult, who was born and spent his formative years in Pena Duro, the prison colony of Santa Prisca, and now as a man who still considers Santa Prisca his home, Bane is Latino by nationality as well.
What would happen if you were to take Bane's mask off? “It would be extremely painful…for you.” Here, Bane says that it's not a good idea to mess with him, that any pain you might inflict on him, he'll return two-fold. Throughout the film, we see that Bane is a man of his word, and is never to be trifled with.
What will happen when Bane takes off his mask? It causes him a lot a pain, his mask is constanly giving him pain killers in the form of a gas, so taking it off would make him feel a lot of pain.
While fans got to hear many memorable quotes from Joker in Batman: Arkham, the series also revealed what his greatest fear is supposed to be. As it turned out, The Joker feared being forgotten more than anything else because it meant nobody was afraid of him anymore, rendering all his crimes void.
Due to a harsh childhood in which he was intimidated by his physicality and his passion for studies, Crane develops a kind of obsession with taking revenge through fear. This trauma was never overcome and his withdrawn character mutated into an unscrupulous soul who enjoyed the power that gave him.
If you ask Joker, it's a moot point—as he famously states in Detective Comics #664, a side effect of Joker's tumble into the Ace Chemicals vat is an immunity to all toxins, up to and including fear gas.
However, Scarecrow did not want to simply kill Batman but destroy everything that he stood for, take away his allies and family, and ultimately unmask him for the world to see him as just a man before he destroyed Gotham and attacked the entire world itself with fear toxin.
It really depends on which storyline/backstory you're going by. Some say he's afraid of crows, some don't really give him a specific phobia — and I think Bruno Garcia's answer covers this part quite nicely — but in a recent storyline it seems the only thing he's still scared of now is the Batman.
Though the zap from the shock collar stopped Croc from eating Scarecrow, he still refused to let go, and dove back into the water with a screaming Crane in his grip.
