http://shmuplations.com/dqivroundtable/
In this lengthy interview from the 11/89 issue of Famicom Tsuushin, Dragon Quest creators Yuji Horii and Koichi Nakamura talk about the challenges of making Dragon Quest IV, with a particular emphasis on the AI system.
Although the later ports of DQIV would add a manual control option, for its time, the party AI system was an impressive new addition to console RPGs—and something of a programming challenge given the speed and memory constraints of early Famicom hardware.