Microsoft Excel is known by many in the field as the grandfather of business intelligence. This may very well be due to the fact that your grandfather was a member of the first generation of analysts to use Excel. All kidding aside, for many years within the corporate world, Excel was the primary tool used to analyze data from a data warehouse as well as to build reports. This is due to many reasons but primarily due to the fact that almost all companies have licenses with Microsoft and so analysts, developers, and managers can conveniently access Excel's capabilities with minimal effort. Specifically, it is difficult to imagine a finance department not leveraging some form of reporting with Excel.
In the last 20 years there has been a conscious effort to push users away from establishing a BI platform built on top of Excel and instead to move towards other tools, which will be discussed in more detail later...