Control-Alt-Delete is a very popular keyboard shortcut for rebooting a Windows PC, NT logon or for invoking the Windows Task Manager in XP systems.
The time saving Ctrl+Alt+Del keyboard combination was designed by David Bradley, a designer of the original IBM PC.
Bradley originally designed Control-Alt-Escape to trigger a soft reboot, but he found it was too easy to bump the left side of the keyboard and reboot the computer accidentally.
He switched the key combination to Control-Alt-Delete, a combination impossible to press with just one hand.
Bradley did not intend Control-Alt-Delete to be used by end users - it was meant to be used by people writing programs or documentation, so that they could reboot their computers without powering them down. But the key combination went on to become a cultural icon especially for hiding the Windows 95 BSOD.
David Bradley describes how he invented CTRL-ALT-DEL - Quicktime Video
Read more about David Bradley at Wikipedia.