This is one of the most important steps that you need to create a wonderful fantastic fantroll! Without a background noones gonna know about your little baby angels life, that you created and basically gave birth to from your pencil or computer screen. Give them a horrible or wonderful past, make their personality correspond to that past, do whatever it takes to make this damned fantroll be....well a fantroll! Vriska had a past, Karkat had a past, even feferi had a past! And guess what they're personality were ALL effected by it. Don't rush their past or trust me it will be horrible. Be careful and precise on their past or it will come back and bite you in the arse I promise.