Where 'Dragon Quest Monsters' originated from was 'Dragon Quest V,' where you had a monster befriend... - Yuji Horii Quotes from quotely.org

Where 'Dragon Quest Monsters' originated from was 'Dragon Quest V,' where you had a monster befriending system as a main part: you could actually befriend monsters and have them fight on behalf of your party, as part of your party.

Yuji Horii