The first Stig was Perry McCarthy, a British racing driver. Since Perry stopped there have been a number of people playing the role. Wikipedia has some more detail.

Sometimes the Stig is the test driver from the car company whose car is being tested.

I do still enjoy Top Gear a lot. There are however too many silly items at the moment. Although some of the silly items are absolutely wonderful, the series of pieces trying to destroy the Toyota pickup were brilliant and the Robin Reliant one last series was one of the funniest things I have ever seen.

I'm not sure we can judge the current state of Top Gear on the last series. They were recovering from the nightmare of Hammonds crash and the filming schedule must have been really screwed up. Even Clarkson expressed frustration after the end of the series that they didn't actually cover many cars.