Douglas Engelbart, the creator of the computer mouse, passed away a couple of days ago. Considering the ubiquity of the mouse as an input device (or "human interface device", as they are called now), it's a remarkable legacy. Digital computers had been associated with a keyboard interface, and the QWERTY keyboard itself is a holdover from the days of the typewriter (remember those?). The first computer I recall seeing with a mouse was an Apple Mac (with a black and white display!), but the interaction of a mouse-controlled pointer on the screen was fascinating - and more to the point, made sense. The grandaddy of all mouse-based graphical interfaces was actually found on the Xerox Alto (below, with clunky-looking mouse).
Before the mouse, there was experimentation by others on the "trackball" as an interface device - the trackball being like and upside-down mouse, where the ball is rotated by the user's finger, instead of sliding the mouse around to move a ball on it's underside. If you ever played the arcade game Missile Command, then you have used a trackball. The dust- and crud-collecting mouse ball has been replaced by laser sensors on contemporary mice. While PCs have typically used mice with two or more buttons, Apple have long used single button mice, but the general operating principle is the same.