Greek gods

[Dicart]

What we do know is that Homer mentioned Iapetus, stating only that Iapetus dwelt in Tartarus.
The best we have is fragments of fragments and snippets of fragments.
So we are left with a single source for "Great Iapetus"
ergo, the question: "Why great"?

Perhaps because for latin writers like Virgile, Iapet or Japet is classified among the Giants and he is a creation of the titan Gaia (earth) self, or for writers like Hygin he is a Giant created from both Gaia and the Tartare.
Source (in French) found here : https://fr.wikipedia.org/wiki/Japet_(Titan)