I think there were a few stigs. He's just the one who outed himself i believe
1st Stig wore a black suit, he appeared in the first 2 series, then the media found out who he was, so they sent him off of an aircraft carrier in a nitrous-powered Jag.
2nd Stig, Ben Collins, wore a white suit and appeared on Top Gear from 2003-2010. His identity was kept secret until he published his autobiography, titled "The Man in the White Suit."
3rd Stig (also in a white suit) has been on TG from 2010-present, identity unknown.
And of course, all of the Stig's various cousins...