One example is Icelandic sagas. Two of the most famous such are Egil's Saga and Njal's Saga, bearing personal names. Others, such as Laxdæla saga have place names in their titles.
The examples of the Iliad and Odyssey from another cultural tradition show the same mix: place name and personal name, respectively, in this case.
In classical Greek literature there are works with titles like Antigone, Philoctetes, and so on, named for people, and (from the same author) Women of Trachis naming a place, and Oedipus at Colonus naming both a person and a place. A different writer gave us Electra, Andromache, Hecuba, and The Trojan Women, with all but the last naming people; yet another gave us The Persians, Seven Against Thebes, and Agamemnon, naming places and a person. Another used Lysistrata, The Frogs, and The Clouds, naming a person, a kind of animal, and a natural phenomenon.
Zipping forwards a few millennia we have The Magic Goose of Cairo and The Marriage of Figaro, naming an animal, a place, a ritual, and a person.
Then there are the classical pansori works with personal name-derived titles: Chunhyangga,
So across the world and across time literary works have borne the names of people and of places. Is this a trend, a trope? Examples of the sort listed above could be multiplied, but without understanding more precisely what you are really asking, I'll forbear.
Or maybe you are asking for when the word "saga" was used to mean "the story of", as in titles like The Forsyte Saga or The Herries Saga or the generic AGA Saga. In the 20th century, I'd guess. When did the word begin to be used to mean "long story" in English? Numerous citations in the OED suggest the 19th century. I would further guess that this was under the influence of the 1816-1818 Deutsche Sagen by the brothers Grimm. Nowadays the term is a staple in the word-store of the writers of jacket-blurbs.