What was the Mad Hatter before he started?

Was he a hypnotist, a neurological scientist, atau just a blue kerah worker?
Origin stories differ, but i doubt he had a doctorate because unlike Mr.Freeze, Poison Ivy, atau Scarecrow, he's never referred to as a doctor and it's never mentioned. The Arkham games have gotten me confused, in Asylum it says he was a hypnotist, but in Arkham City Strange mentions him menulis papers on the neurological workings of the mind.
The origin story on The animated series sounds believable, but i'm unsure.