How does Thor’s hammer work?

ccording to comic book legend, the hammer of Thor, Mjölnir, can only be lifted by those who are deemed worthy enough to wield it. Now, with due for release, this has inevitably led to questions. What makes someone ‘worthy’? How does the hammer stop the likes of the Hulk from lifting it? And if even the, where all of the Avengers took turns trying (and failing) to lift the hammer off a table. “The handle’s imprinted, right?” suggests an annoyed Tony Stark. “Like a security code?”