M.U.L.E. was written by Danielle Berry (then Dan Bunten) and was released in 1983 on both the C64 and the Atari 800. Dan was also the author of Heart of Africa and Seven Cities of Gold, mentioned above, as well as Robot Rascals, Modem Wars, and Command HQ.
Danielle had scaled back her game design work following sex reassignment surgery in 1992. Sadly, Dani Berry succumbed to cancer in July of 1998. She was 49 years old.
There are several shareware clones of M.U.L.E. currently available or in development. For fans of the game, consider the possibilities of online play - cramming four people at that C64 keyboard was a pain!