Here is a link to the backstory that this site heleped develop for me last year.
Having now played this character for half a year I think the most important thinig is to have an arc for your characters moving forward, rather than backward. To some degree my GF and I/the people of this forum planned out the first half of a tragic love story - which gives the characters a sort of anchor/motivation for all of the other things they do.
As @Geoffrey_Willoughby says, they generally become largely irelevant as soon as you hit the field. The exception to that I think is if in your group you can create interesting dynamics - like our tragic love story. This means that your backstory isn’t something that you sit round hoping for someone to ask about- but is continually embodied.
A less convoluted dynamic could be maybe that two of your group are constantly trying to outdo one another- in drinking, in fighting etc. In my opinion whats best is to create dynamics that are fun to do and fun to watch for the people around you. This makes people want to get involved with your characters and their stories.
My impresion is its easy to lose your characters backstory in the game - because the 3000 other players don’t know or care about it- but everyone cares about coin and battles etc. I almost thought of Tristram/Unas/ their relationship as having handles - things that would be easy for other people to grab onto and run with - and other people getting involved makes the backstorys feel real. As soon as your outdoing each other brothers have other characters taking sides and chearing them on it suddenly makes the characters and their relationship 3d and solid.
I would have given up on all of Tristrams convoluted tragic past -had i not had so many great people around me feeding into it and enlivening different aspects of it. Whilst a lot of that came from the general goodness of their hearts - a lot of it was that there were things someone on the outside could enjoy and get involved with if they wanted to.