According to Peter Mattis and Spencer Kimball, the original creators of GIMP, in their announcement of GIMP 0.54:

The GIMP arose from the ashes of a hideously crafted CS164 (compilers) class project. The setting: early morning. We were both weary from lack of sleep and the terrible strain of programming a compiler in LISP. The limits of our patience had long been exceeded, and yet still the dam held.

And then it happened. Common LISP messily dumped core when it could not allocate the 17 MB it needed to generate a parser for a simple grammar using yacc. An unbelieving moment passed, there was one shared look of disgust, and then our project was vapor. We had to write something... ANYTHING ... useful. Something in C. Something that did not rely on nested lists to represent a bitmap. Thus, the GIMP was born.

Like the phoenix, glorious, new life sprung out of the burnt remnants of LISP and yacc. Ideas went flying, decisions were made, the GIMP began to take form.

An image manipulation program was the consensus. A program that would at the very least lessen the necessity of using commercial software under “Windoze” or on the “Macintoy”. A program that would provide the features missing from the other X painting and imaging tools. A program that would help maintain the long tradition of excellent and free UNIX applications.

Six months later, we've reached an early beta stage. We want to release now to start working on compatibility issues and cross-platform stability. Also, we feel now that the program is actually usable and would like to see other interested programmers developing plug-ins and various file format support.