GIMP was started as a project by two Berkeley students called Spencer
Kimball and Peter Mattis. It was first meant as a university project that
they received credit for.
GIMP used Motif at first but Kimball and Mattis later developed
Gtk+, so it can be used as its underlying
GUI library instead. Since then, Gtk+ has become the basis for many other
projects including GNOME.
GIMP 1.0 was released several years after the switch to Gtk+, and GIMP 1.2
(which already used Gtk+ 1.2) was released three years afterwards.
Since then, the GIMP has acclaimed many fans and it is considered the most
complete and active image manipulation programs for UNIXes to-date.
GIMP 2.0.0 was released in April 2004, featuring a port to Gtk+ 2.0, an
improved user-interface, a general code cleanup and modularization and
many other improvements.
GIMP 2.2.0 was released in December 2004. It is backwards compatible
to GIMP 2.0.x, and featured various improvements, additions and cleanups.