With all the talk lately about starting new characters once the Cataclysm arrives, it struck me that most roleplayers already have more than one, including myself. Like most players, I started with one, a night elf druid, and focused on playing that exclusively for quite some time. It didn't really occur to me that I would even want to play more than one.
Then, I began to notice that other people played more than one character, even within the same small group of friends. I had one friend in particular who had mastered the art of roleplaying multiple characters. She never said anything out of character to anyone in our group, and it took me ages to even realize that her characters were ally played by the same person in the first place. Each one had its own personality, and each had a different relationship with all our mutual friends.
Knowing her made something click inside my mind, and I began to see other possibilities for myself too, other sorts of characters I could play with different weaknesses, strengths, and entirely different stories to tell. As my roleplaying experience grew, I began to feel as though one character couldn't contain all the ideas I had jumbling about in my head, so... I started another one, then another, and ... another. Little did I know all the pitfalls I could run into with so many characters, nor the quirky little tricks that could become possible with multiple characters, a small group of friends, and a bit of creativity.
Same great friends -- new intertwined stories
I should be clear, when I talk about "the art of the alt," I mean on the same server, with the same group of friends. If you play multiple characters on different servers, factions, or even different guilds on the same server, then that will be a different experience. Roleplaying multiple characters in multiple social spaces is like playing just one character, except it takes more time, and you get more varied experiences. Roleplaying multiple characters with the same group of people is a bit like having a whole cast of characters in a TV show, which you and your friends can collectively improvise with.
Usually, everyone's first character is one people play for their own reasons, whether they like the class, the character style, or even have some sort of backstory in mind. Without working with multiple characters in a single group of friends, though, a first character is usually going to be a lone wolf in one way or another -- all his or her friends and family are perpetually off stage, since there is no one else around to play them.
But once you find a group you really like, you or someone else in your group may decide to start a new character who is already connected to your first in some way -- or perhaps you decide you'd like to do that for someone else. They may be siblings, teacher and student, or even parent and child if the characters' ages work out alright. Sometimes this new character is one you've already been thinking about for a while and only recently decided to connect to a friend of yours in the guild; and sometimes it is completely inspired by something that came up while you were roleplaying together in the game. Either way, the connections you set up between you can be a great inspiration for roleplaying.
To be (your own brother), or not to be -- that is the question.
If you play the related character yourself, then you have more control over the connections between them, but you can't easily let them both be in the same scene together; for this reason some people create reasons for their characters to be apart most of the time, such as a grudge between brothers, or even just being busy in different places. I usually connect my characters only loosely, possibly through some kind of activity that they may share offstage. For example, my gnome character instructs my draenei character in engineering -- their classes happen elsewhere, and it makes sense that even though they might not be in the same place at the same time in front of the other guild members, each one can still have an effect on the other, and each one can play a different role in the same guild story.
Letting different people play related characters opens the doors for more interaction between them. One of my guildmates told me of a story in which he was roleplaying a draenei whose memory had been damaged in the process of becoming a death knight, and teamed up with another guild mate to help fill in some of his character's back story. She made a new draenei hunter to be his daughter from a previous relationship in his past. It just so happened that while they were making this plan, a different guildmate's character got started in a new romantic relationship with him, so it was a big thing for the new couple to discover he had a full-grown child from a forgotten past.
These interconnections between characters can drive a lot of the roleplaying plot forward, but if you want to play them seriously, alts can take up a lot of extra time, especially if you roleplay a lot instead of leveling. Having many characters is great for those people who either aren't particularly interested in maintaining them all in endgame activities, or else have a lot of time they can spend.
Multiple personalities -- simultaneous entertainment!
Now, one thing you can do when you have multiple characters is not for the absent-minded, or feint-of-heart, or overly forgetful people in the roleplaying community. Some roleplayers have found that it works well for them to roleplay several characters all at the same time -- that's to say, without logging out of one character and into another. Instead, they pick whichever character they feel is most appropriate and then they write the name of whichever character is speaking in brackets, so that it appears before whatever they say as a normal character's name would in the roleplaying channel. It looks a bit like this:
[Davidicus] says: I'm the leader of this group. I decide when we stop and have a snack.
[Ammarina] says: I'm tired. And hungry.
[Davidicus] says: You are, sweetie? Then let's stop everything and have a snack.
[Davidicus] says: [Fizzlebolt]: Ugh! Where's my mind-control helmet?
Another way to do this is as if it were a novel, describing what both one's characters are doing in prose format, even if other people in your group are not doing so:
[Ammarina] says: Laurilel shifts out of cat form, tries to look innocent, and says, "Me? I wouldn't dare! Besides, I don't even like chocolate." Her mouth still has a trace of dark chocolate on her lips.
[Davidicus] says: Erm... Here, sweetie. You can have some of mine...
The main problem with both of these methods is, of course, that all this can be hard to keep track of, both for readers and for the person speaking multiple roles at once. It's important that everyone participating in the roleplay is willing to give it the extra attention to figure out what's going on. It certainly isn't a trick for new or very casual roleplayers, but if you play with a pretty experienced group and you want to give it a try, you might find it rewarding.
Secondly, this method only works when you're using a system like a "guild hall" we discussed previously, where all the roleplaying is taking place in an imaginary place all the characters can share, regardless of what they're actually doing in the game at any given moment. It obviously wouldn't work to try and roleplay multiple characters at once in the "Say" channel we use for more conventional roleplaying when our avatars are actually in one spot together. Warlocks, hunters, and death knigths, can use an addon like PetEmote to roleplay their main characters and their pets at the same time, but that's pretty much the extent of what you can do unless you decide to get into multiboxing.
Incidentally, multiboxing is just what my old friend eventually learned to do -- the same one who originally commanded her multiple characters so skillfully that I was inspired to do the same. She figured out how to synchronize the actions of her identical quadruplet sisters so that, in addition to fighting the way most multiboxed characters do, they could all walk, bow, laugh, and talk separately or at the same time. She quite literally played all of them simultaneously in a way that astounded everyone they met, and it was a blast for everyone.