David J. Bradley is credited as being the original inventor of the ctrl-alt-del control sequence (see also ctrl+alt+del). David was, and still is (2003), a employee of IBM. He was one of the 12 original engineers working on the first IBM PC, the 5150.
Somewhere in 1980 or '81 he introduced the key sequence as a useful tool for people writing programs and developing instruction manuals. Apparently he didn't ever intend it to be open to users and surely didn't forsee it's widespread use in modern day computers. The original idea was just to provide users with a way of resetting their PCs with out having to physically switch it off. He chose the control and alt keys since he needed two shift keys to make the operation work. He then chose the delete key (situated on the otherside of the keyboard) to prevent users from accidently resetting the computer.