In my experience, having "kinky alter egos" is a pretty common thing. For example, when we're sceneing my boyfriend becomes Master and I become kitten. Many of my other partners have names for their alter egos as well, at least the dominant ones. (For a long time I was almost exclusively submissive, so their own subbiness didn't get much practice with me.)
But I've noticed an interesting difference between me and a few of my partners in terms of how we relate to our kinky sides. They refer to their alter egos in the third person, almost as if they are separate people. "Lupa is very mad at you," my friend will growl sweetly, hinting at what will come later that evening. Even more interestingly, Ume's alter ego Jack comes up in places other than the bedroom; he says that he finds Jack useful when playing poker and he must find the right balance of being a cutthroat risk-taker and a prudent observer of people's behavior. Jack is certainly a useful persona; he's earned his rent check (and then some) many times that way.
I didn't think much of this until recently, when playing with Lupa and Ume. I recently worked up the courage to express my Domme side around Ume, to the great delight of us both. (Domming a man who's significantly bigger than me has been a fantasy of mine for a little while.) While Lupa and I had fun tormenting him, he suddenly asked, "Do you have a name you want me to call you?"
I paused. "You know, I haven't actually thought of that," I admitted.
"Is what I've been calling you so far okay?" he asked, having been calling me Mistress up until that point.
"Oh yes!" I said, and we continued with our fun. It certainly made me feel in charge, and I don't call Master anything other than Master, so Mistress was sufficient for me.
Later, Lupa asked Ume if it'd be possible to "talk out" Jack. I was curious; though he'd taken a dominant role in our playsessions before, I had never noticed a distinct persona, like I do when Master is Master. So we started bantering, references to gambling and luck being prominent in our innuendo. As Ume explained the difference between himself and Jack, I could see the shift in his body language and in his speech patterns as he began to settle into Jack's mindset. However, I was still in a Dommy mood myself, and I couldn't bring myself to be properly "afraid," even though I could see that hungry gleam in his eye. Instead, I kept teasing him - being a real brat. "So," Ume finally asked me, "how are you going to make good on our bet?"
"Well," I said with a grin as I lounged on the bed, "I guess you can just tell me what to do, and I'll fulfill your request to the best of my ability."
He looked me up and down once, again with that predatory gleam. "Good," he said. He pinned me down to the bed and kissed me - and I immediately could tell that this was Jack. Whereas normally Ume's kisses are incredibly gentle - I'd even call them tentative - this kiss was forceful, hungry, and confident. He knew what he wanted, and he knew he could take it. And, like flipping a switch (HA HA I MADE A FUNNY) I was suddenly in full-on submissive mode.
This was the first session where I've switched from Domme to sub like that (and where my partner has done the same), so I think that's why it got me thinking about alter egos. I certainly have different behaviors, speech patterns, etc. when I'm kitten (instead of everyday me), but I don't really think of "kitten" as separate from "me." But then again, "I" would be fucking pissed off if someone called me a slut or a cocksucker, where as "kitten" loves it. Would it be helpful for me to think of my submissive (and my dominant) personality as separate personas? Or would that lead to unhealthy compartmentalization? I don't know. I'll have to think about it more.