First establish an environment - objects inmate or alive. Establish role models. Base first character on how they would act with such role models in their environment. Second character would have a relationship with first character different role model and same or different environment. Continue to create character based on first until last and soon you should have a complex community of unique characters.
A good place to start- Free Trial: https://marinersoftware.com/products/persona/
A good place to start- Free Trial: https://marinersoftware.com/products/persona/