The Stig is a well known unknown person. No one knows his identity. In fact, there are multiple of these Stigs, and when one of them gets exposed (Ben Collins, Michael Schumacher, and many more), another takes his place.
Some say he thinks the Ariel Atom V8 is a microscopic being that lives in engines. All we know is, he's called the Stig and he knows how to drive like one.