Although Zeta spends most of his time in the guise of Zee Smith, it is sometimes necessary for him to take on a younger form- after all, as Ro says, most adults don't pay much attention to other people's kids. Zeta can alter his hologram to look like a younger version of Zee- about ten years old or so. To distinguish between the two Zee's I've labeled the younger Lil Zee- for your convenience, of course. ;)

While Zeta's profound naivte seems a bit strange on an adult it only makes Lil Zee look cute and curious. It also gives him a chance to examine the basis of 'fun'- a concept which he finds greatly confusing (especially since Ro's idea of fun is more than a little skewed when compared to the general concensis). Another advantage to being Lil Zee is that when he asks delicate (and unknowingly rhetorical) questions, people are more likely to humor him with a response; they write off his oddness to the inexperience of childhood and don't ask many questions in return.

When asked about their relationship Ro usually claims Lil Zee is her younger brother. They don't look much alike but Ro's irritation with his antics usually cements the general concept of sibling behavior. Though Zee doesn't spend a lot of time in this form it's a very fitting- and entertaining- personality for him.