The Aston Martin DB4 GT Zagato was introduced in October 1960 at the London Motor Show. It was effectively a DB4 GT, lightened and improved by the Zagato factory in Italy, by Ercole Spada. Initially the factory had plans to produce 25 cars, but demand was not as strong as expected and production ceased at the 20th unit. Nowadays, due to the rarity and popularity of the DB4 GT Zagato, the cars are worth a considerable amount of money, and at auction they reach well in excess of £1 million.
The popularity of the original DB4 GT Zagato has resulted in two subsequent waves of cars based on DB4s being rendered into "Zagatos" through the cooperation of Aston Martin and the Zagato works in Italy. They are known as "Sanction II" and "Sanction III" cars. Also, an unauthorised but lucrative private industry of modifying original DB4 GTs into "Zagato" replicas has arisen as well to meet market demand for high-quality Zagato recreations.
Source: Wikipedia (original)