I'll include some links in this post, but the short answer is that The Stig is a character created for BBC television's Top Gear. He is a professional driver who races all the reviewed vehicles. The Stig's costume, a nomex racing suit and helmet, naturally obscures his identity which has been the source of endless speculation and series features about who - or what - The Stig is.
Since The Stig can be anyone, there is no reason The Stig could not be me. Therefore I ask that you kindly refer to me as Mister Stig. (You get brownie points if you catch the famous movie reference.)