Whether you have many alts or just a few, do they know each other? Do they have some sort of relationship as people living in Azeroth, or is sending materials and money between them just a game mechanic for you? If your characters do know each other, what kind of relationships do they have, and how did those relationships come into being? If they don't, what functions do your different alts serve?Despite never RPnig in game (except once in a serious context, which was actually incredibly awesome and should probably be discussed), you may have noticed in the occasional story post that I do think about the personalities and lives of my characters. They are more than raid tools to me; they provide a constant source of creativity, especially now that I have left behind the anime-related fanfiction of my youth and the even older Standard Fantasy stories that I wrote in my childhood.
The short answer is yes, my characters know each other. The long answer is that the relationships are different for each.
To start, who are my characters anyway? Hopefully by now you know my main, the druid called Akabeko. Since I don't like using guildies as characters in writing, I tend to assume that she is "guilded" with my more oft-played alts in addition to actual guildies, so I can have her interact with someone as a comrade-in-arms. Those generally turn out to be my paladin Iharu and the irritable warlock Maurene. Although I tend to think of each of them as having very independent lives due to the pressures of being a hero, they also are inexorably drawn together to relax, argue, strategize, and solve mysteries Scooby-Doo style. The different races especially give a great source of clashing views and opinions and make for fun "odd couple" interactions. I love having the conservative (ex-human) Maurene get crabby around the snarky, sexy paladin, with Akabeko as a mediator.
Strangely, I don't know if I've ever really thought about how the trio came together in their current relationship. I have a very old scrap of writing in which Akabeko visits the Undercity for the first time and, while stumbling around and flipping out about demons in plain sight, encounters Maurene, who is trying to peddle her enchants. Maurene gives her an enchant of some sort, taking pity on the poor country bumpkin, and sends Aka on her way. Since then, every story I have written about them has started with the assumption that they all know each other. Sometime between their "origin" stories and their together-time stories they have come together without my knowledge.
Then there are my goblin(s) who will eventually know each other in an upcoming episode of goblin Journal! Despite being a very new character, Sprinkie the mage has really grown on me, and the more I write about her the more I learn about her character. After creating a goblin hunter (in order to save the uncontrollably awesome name Myda), Sprinkie's story suggested how they could come to meet, and I look forward to writing all of that.
When I think about the stories that center around the two Horde groups, I get the feeling that although the characters might know each other in passing or in rumor, they won't interact directly all that much.
Bank characters aren't left out either, and I've even had some fun imagining the life of a bank toon. I set it up as merchants who take on clients whose auction house affairs they manage. (Basically, an auctioneer that I control). My first bank toon was a tauren druid (to ensure I would never want to actually play the character), and I had a fun time figuring out why a tauren would be interested in handling money and business, and how that might affect her personality and interactions with others of her race.
There are two characters on my current server that I never thought about one way or another, and they are my DK scribe and my rogue lockbox-farmer. You might think, well clearly, with purposes like that, why would you have bothered to think of any sort of history for them? The weird thing is that on my old server I had a tauren banker and an undead rogue, and both of them got at least a second glance at a backstory. These two characters, for whatever reason, have managed to grow up without so much as a last name.
Alliance-side, I only just expanded from 1 to 3 alts, so I haven't really had a chance to think about those characters or their interactions. I think cross-faction interaction will be limited to an easter egg passing mention.
Now I'm thinking a lot about my character personalities! Quick, to the blogmobile!