To add on, something that made the companions from BG1 and BG2 iconic was their easily identifiable traits. These characters are Edwin (extreme narcissist who constantly talks under his breath), Minsc (a ranger with childish concepts of good and evil who travels with a miniature giant space hamster), Tiax (comic relief whose entire character is defined by his delusions), Jan (bizarre gnome inventor that acts like a snakeoil salesman), Ajantis (Overenthusiastic #1 Helm fanboy "By Helm! Yeah! Helm, give me strength! Yeah!"), Viconia (exiled drow coming to terms with culture shock), etc.
It's good to make three dimensional characters, but easily-identified defining traits can help make memorable characters.
