A Stradivarius is a type of string instrument that was made by the Italian luthier (instrument maker) Antonio Stradivari during the 1700s. He is known for making some of the best and most valuable string instruments in the world, so these instruments are highly sought after. They are made from the best quality wood and Stradivari used special techniques to give the instruments their unique sound. They are usually valued at hundreds of thousands of dollars due to their rarity.