What company or individual is responsible for developing the windows operating system?

The Microsoft Corporation, founded by Bill Gates, is responsible for developing the Windows Operating System.

History:
The Windows Operating System was the first operating system (OS) that provided a GUI (Graphics User Interface) over the previous Disk Operating System (DOS) for personal computers (PCs) in 1985.
Initially, the GUI provided cooperative multi tasking, which means that only one software application could run at a time.

Consequently, many releases of Windows OS followed that provide pre-emptive multi tasking, which allows many processes to run concurrently under the supervision of a process manager, which assigns priorities to individual tasks.

Currently, the Windows OS is a sophisticated PC based OS that runs on over 90% of PCs. It provides preemptive multitasking, network communications, internet access, disk management, print management, cloud based applications, and much more