Learn Italian: Il dio disse una parola divina e l'eroe nacque. - The god said a divine word and the hero was born.

The passato remoto is used for completed events in the distant past, especially in literature, history, or myth. A sentence about a god (il dio) and a hero (l'eroe) has a strong mythological, storytelling feel, making the passato remoto the natural choice over the passato prossimo.

What verb does disse come from, and how is it conjugated in this tense?

Disse is the lui/lei form of dire (to say). In the passato remoto, dire follows a very common irregular pattern. It uses an irregular root (diss-) for the io, lui/lei, and loro forms (dissi, disse, dissero). The tu, noi, and voi forms are built on the regular root (dicesti, dicemmo, diceste).

The English translation says "was born", which looks passive. Why is nacque only one word?

In English, "to be born" is a passive phrase. In Italian, nascere is simply an active, intransitive verb meaning "to be born" or "to come into existence." Therefore, you just conjugate the verb directly rather than using a helping verb. Nacque is the active passato remoto form for "he was born".

How do we conjugate the rest of nascere in the passato remoto?

Just like dire, it alternates its roots. You use the irregular root nacq- for the io, lui/lei, and loro forms: io nacqui, lui/lei nacque, and loro nacquero. The other three forms use the regular root nasc- and regular endings: tu nascesti, noi nascemmo, and voi nasceste.