Apple from the mid-1990's to present. CEO John Sculley had been instructed in 1993 to sell the company (unsuccessfully, to AT&T, IBM, etc.), before getting fired. He refers to the time as Apple's "near-death experience." In 1997, Steve Jobs returned to the company via NeXT and Microsoft invested a severely needed $150 million. Without those two events happening, it is highly possible that Apple would not still exist today (let alone being the most valued technology company in the world). That's about as radical of turnaround as possible.