Here's the winner of our contest:

AMBIGUGUS, The Remarkably Unmemorable Man, suggested by Jon Harmon
Okay, here's what I was thinking (and if you need to read this section, then I have failed you, reader. I am sorry). I was originally thinking of giving him no features at all, like the old Dick Tracy character, The Blank. Of course, it bothered me that if any of us really saw a featureless man, he would be the most remarkably
memorable man we'd ever encountered. So, apart from making his features a little indistinct, I decided to put him in front of three mirrors, each of which is reflecting something entirely different. He's unmemorable because, each time you look at him, he appears as a completely new person or thing.
Ta da.
Thanks to everyone who submitted a name or voted for one! And thanks to
Cyril for putting the idea of reflections in my head.