in 2e I had a Ranger that started as first level as a quasi multi class (spell fire from Volo's guide). I had established when the character was made that as I found out more about my 'gift' I would want to become more invested in magic and duelclass at some point to wizard unless the campaign went way crazy (it did but I still did around level 7ish).
My background could be summarized in a few paragraphs but I wrote it as 11 pages (yes wrote not computer typed). It also involvoed 2 other PCs who each wrote there own back stories (one much shorter and one much longer then mine). of the 7 players at that table we all had some form of background. It was all worked out with the DM, and worked into the story and as such it worked well.
I knew the fighter and the wizard/thief from my background, he (fighter) grew up in the town near the farm my (who i thought was my) family owned, and he was a bully who used to pick on and beat me up as a kid (I was a half elf he was human). She (Wizard/Thief) was the only of the 3 of us that WANTED to be an adventurer... she was someone we both competed to impress. By the time we were all late teens early twenties she had run off to adventure, he had been drafted into a local small war, and I was firmly in the mind he would just be a farmer...maybe someday own the family farm... then the red wizards AND a f ing beholder showed up destroyed his family home and tried to kidnap him until an old man that he didn't know saved him, and sent him to a bar... and that bar was the first game us all meeting, and the fighter apologizing to me, and both of us to her... and meeting 4 other people who all had an old man they didn't know some how get them to come to the bar... oh, and I had to admit at that point I knew I was being hunted.
our backgrounds MADE that game.