[Leigh Butler]
Taim is not Demandred in disguise.
How do we know? Because RJ said so.
Q: "It's been said that you mentioned that Mazrim Taim is not Demandred. There seems to be some confusion on whether or not you said that."
A: "Mazrim Taim is not Demandred."
[Matthew Julius, post-COT signing, Dayton, OH, January 16, 2003]
Tim Kington concurs:
Q: "Taim is clearly not Demandred, right?"
A: (Disgusted) "I've said that before, and it's not Taim, it's Ta-eeem."
The same response was also reported on wotmania.com, in LiveJournal's Wheel of Time community, and in several emails.
We have multiple reports from multiple independent sources all saying the same thing; evidently RJ felt that the counterevidence provided in WH (the double set of orders to the renegade Asha'man, Demandred's failure to recognize Flinn at the Cleansing) was sufficient to answer the question, and decided to stop beating about the bush on the subject. That effectively closes the topic as far as I am concerned.
FAQ policy has always been that the author's word is canon. If RJ says a thing is so, it's so. And with that I'm afraid the die-hard Taimandred fans will have to be satisfied.
(See section 1.5.6 and section 1.4.10 for more discussion on what Taim is up to.)
We don't know.
There have been a lot of names bandied about as possibilties; Bashere, Masema, and the mysterious Taraboner seen in Arymilla's entourage outside Caemlyn [COT: 15, Gathering Darkness, 371] seem to be the most popular.
All of these can be debunked or contested for various reasons, but it's not necessary to do so:
Q: "Have we yet seen the alter ego Demandred presents to the Third Agers on-screen?"
A: "No." (I asked twice to make sure.)
[Michael Martin, Dayton OH signing]
So, if Demandred is disguising himself as someone, it's not someone we've met in books 1-10. He might appear in either Knife of Dreams or The Gathering Storm, but hasn't done something suspicious enough to put us on his trail.