In 2007, I was spending a my norther-hemisphere summer experimenting with UI automation. Born of those efforts, xdotool came into being when I separated it from another project. The goal was modest - write some scripts that execute common keyboard, mouse, and window management tasks.
The first commit had only a few basic commands - basic mouse and keyboard actions, plus a few window management actions like movement, focus, and searching. Xdotool sprouted new features as time rolled on. Today, the project is 18 years old, and still going!