Microsoft is in one of the most challenging periods in its 38-year history, and Steve Ballmer — its CEO for the last 13 years — is on his way out. In August, Ballmer announced that he'll retire just as soon as the company finds his successor. The decision comes after a major reorganization that aims to turn Microsoft into a "devices and services" company.

The challenges the company faces are massive: Windows 8, Windows Phone, and Surface tablets have each so far failed to find the blockbuster status that the PC-dominating company was once known for. And it's taking on the phone division of struggling Nokia, with a $7.2 billion bet that it can make its own smartphones without alienating hardware partners in the process. The path forward isn't clear and Ballmer is leaving with a mixed legacy. However, two things are clear: Ballmer's charismatic and passionate leadership style is one of a kind, and Microsoft's next boss will take the reins at an intensely difficult time.