Vista Eyes

xeyes is a graphical computer program showing two eyes which follow the cursor movements on the screen as if they were watching it.

According to the X Window System manual page, it was initially written by Jeremy Huxtable for the NeWS system and presented at the SIGGRAPH conference in 1988. It was then ported to X11 by Keith Packard. Its popularity is due to the fact that it was run by default at the startup of the GUI in many installations.
Many similar programs have been developed for X and other systems, such as Windows and Java. Vista Eyes is the latest of all.