The Stig's name derives from presenter Jeremy Clarkson's days at Repton School, new students were always called "Stig." A proposed name for the Stig was originally "The Gimp" until protests from Perry McCarthy nixed the idea. There have been two official Stigs on the show, while various other Stigs have made cameo appearances for particular episodes.

The identity of the first Stig (Black Stig) was revealed to be Perry McCarthy when his book Flat Out, Flat Broke was published in 2003

In a Winter Olympics special episode of Top Gear, the Stig was shown doing a ski jump using a snowmobile, the driver performing the ski jump stunt was Dan Lang, a Swedish snowmobile cross driver

The white stig is Ben Collins, its was disclosed and confirmed by the investigation into Richard Hammonds accident, where Ben Collins is described in this legal document by the Health and Safety Executive as someone who worked closely with Top Gear as a high performance driver and consultant.
If he worked closely with Top Gear as a high performance driver, how many reports are you aware of him being in, his contribution is kept secret as he is the STIG.

http://www.hse.gov.uk/foi/releases/richardhammond.pdf