[dasmoth]

"an adjective or phrase expressing a quality or attribute regarded as characteristic of the person or thing mentioned."

Some epithets are negative. But certainly not all.

[wavefunction]

At least in the Homeric epics epithets were used as mnemonic devices for oral story-tellers and their audience to keep track of who was who, like 'swift-footed Achilles':

https://en.wikipedia.org/wiki/Epithets_in_Homer

Apparently the Greeks got this from earlier Indo-European traditions.