What is the proper term for "Heroic Titles?"

In sagas and such, Heroes’ names will often have a description of their major deeds. You have things like “Njarll Bjornson, Slayer of the Beast of Rathgraben” or “Ulfgar, Who Did Journey a Thousand Leagues.”

Is there a term for these little one-line resumes after someones name?

Epithets?

They’re kind of like an epithet or sobriquet, but for longer descriptive titles I’d classify them as a textual honorific.

Stranger

Now I know what to ask for when I change my business car to read, “Hypno-Toad, Reviewer of a Thousand Cases.”

Relating to Norse naming conventions, descriptors were called “bynames.”

https://www.nordicnames.de/wiki/Old_Norse_Bynames

For what it’s worth, the wiki for Epithets in Homer lists stuff like “Raider of Cities” for Odysseus, and “Daughter of Zeus who holds the aegis” for Helen, and “slayer of Argos” for Hermes, who also gets “messenger of the gods and conductor of men”, which seems to be getting pretty wordy.

This type of usage is often a byproduct of the alliterative patterns of the heroic sagas.

Surely you mean Athena, there?

Shirley, I would; but that is how wiki lists it, and so I erred on the side of carefully-worded brevity (though I did take a moment to screenshot it yesterday — figuring that someone might bump the thread with the point you just made, and figuring that wiki might have changed by then to reflect a more sensible answer).