The man is actually a professional editor, journalist and automotive scribe, having penned car-related columns for a number of newspapers and even British GQ. He's written a number of books including one called Life in the Fast Lane: The Johnson Guide to Cars, which appears to be straight from the Jeremy Clarkson school of car comedy. You can read more about Johnson at his official website here, check out his video review of the Nissan Quashqai here, or read reviews of his book at Amazon.com here.
Oh, and Johnson did appear on Top Gear once to drive a reasonably priced car on the TG test track. His time? 1:56 seconds in a Suzuki Liana (this was before they switched to the Chevy Lacetti), good enough for ninth place at the time and ultimately 56th when the list was finally reset. Did your city's mayor appear on Top Gear? That's it, we're moving to Chelsea.