Microsoft originally developed Altair BASIC as the programming language for its first product.
Bill Gates and Paul Allen created the software in 1975 for the Altair 8800, an early personal computer kit made by Micro Instrumentation and Telemetry Systems. Their version of BASIC allowed Altair owners to write and run programs without building machine code themselves.
Microsoft, originally called Micro-Soft, was founded in 1975. Its later licensing agreement to provide MS-DOS for IBM personal computers helped establish the company as a dominant software supplier. Windows, Office, Azure, and other businesses later turned Microsoft into one of the world's largest corporations.
Altair BASIC is not the same thing as Microsoft's later Visual Basic or the BASIC language generally. It was a specific interpreter adapted for the Altair 8800's limited hardware.