Gracious Anthracite @dragon.style some lady that draws comics (http://egypt.urnash.com) and likes to call herself a dragon •••• owner and operator of dragon.style •••• current project: Parallax (http://egypt.urnash.com/parallax/, @parallax)
Mysticism gives us concepts to answer these questions with such as "higher self" or "HGA" or "oversoul" or even "god", and which one you use can raise all kinds of questions.
More mundanely the language of furry is useful for the day-to-day role shifting. My adminsona on dragon.style is deliberately not my usual dragonsona, Gracious Anthracite is designed as someone more patient and serene than my usual dragonsona, and having her icon there next to whatever I'm typing here reminds me of that. My significant other and I have "hatesonas", who are a grumpy married couple along the lines of The Lockhorns; performing them to each other is a good way to say "I am moderately annoyed with something you are doing but I would much rather turn it into a joke and have a play-fight about it, at worst".
And then there are the people who use the language of multiple personalities and describe themselves as "systems". Personally I tend to see that as a warning flag after a few too many experiences with people excusing bad behavior as something done by an "alter", if you have the villain from a popular video game living in your head as a "fictkin soulbond" then it's your responsibility to keep them under control.
Magically, shit also gets interesting when you invite things distinctly outside of anything you would normally think of as part of yourself to *be* *you*. Calling up Osoronnophiris, The Bornless One and requesting something of them is a very different vibe from vehemently *declaring* yourself to be Heart Girt With A Serpent, the one whose Mouth is Aflame, the one who Begets and Destroys, the Bornless One who exists outside of and shapes all time and space, and then *proclaiming* that a thing is so. I dabble in this. I should do it more seriously sometime.
I should really add the Stross and Watts quotes to the front page of the site one of these days. Thanks for the kind words!
(and fwiw my style on that is firmly grounded in 1950s post-cubist cartooning - animation design like Maurice Noble and Mary Blair, album covers by Jim Flora, etc. "Mid-century Modern" is what this vibe has been named in recent decades; you'll find a lot of it in the work of pretty much any GenX animator, especially once digital tools made it super easy to work without outlines.)