Who was Agathon?

Τήν ψυχήν, Αγάθωνα φιλών, επί χείλεσιν έσχον—
ήλθε γάρ η τλήμων
ως διαβησομένη.
-Plato

Kissing Agathon,
my soul was on my lips,
it came forward, poor thing, as if it would cross over into him.

It seems from this verse that, whoever he was, Plato really dug him. Perhaps he hosted more than a symposium at his house.

That verse, some of simplest and most poignant that Plato ever wrote, is remarkably close to modern Greek, notwithstanding that it was composed two-and-a-half millenia ago.