Well, unlike Richard Bachman or Leigh Nichols, Samuel M. Key is an actual entity existing apart from myself. Unfortunately, the separate identity he has is that of a stuffed toy-a small Steiff monkey that I've had since I was a child and who still bears the name Sam the Monkey (from which we get Samuel M. Key....).
Sam's had a bit of a rough life. I carried him about in my pocket when I was a child and he went everywhere I went, losing most of his plush, gaining an ink stain from I'm not sure where, and generally doing his Velveteen Rabbit best to be real. In the years since then, he's managed to find his way into my baggage and accompany MaryAnn and I all over the world.
I've explained why I needed a pen name elsewhere. How I decided on Sam dates back to a long correspondence I had with the late Ron Nance, a dear friend of mine who used to insist that Sam (who has his own rolltop desk and writing paraphernalia in a little "office" on top of my rolltop desk in my office) actually wrote all my books. From there it was a small step further to MaryAnn's suggestion we let Sam have his own by-line.
And just to prove that we are, indeed, two separate beings, here's a photo of the pair of us. Sam's the smaller one, sitting on the cover flat of one of his books.