It was, of course, the iPhone. There are many ways in which the iPhone has defined the modern economy.
There is the sheer profitability of the thing, of course: there are only two or three companies in the world that make as much money as Apple does from the iPhone alone.
There is the fact that it created a new product category: the smartphone. The iPhone and its imitators represent a product that did not exist 10 years ago but now is an object of desire for most of humanity. There's the way the iPhone transformed other markets - software, music, and advertising.