A brief History of Saga.
Saga was originally used to describe Icelandic prose narratives composed in the 12th and 13th centuries.
The word first appeared in English in that sense during the 18th century; by the middle of the 19th century we were employing saga in a somewhat looser fashion, in reference to modern stories involving heroic deeds that bore some resemblance to the Icelandic tales of yore.
By the 20th century saga had come to be applied to other written works, typically a novel or series of novels, especially those that took place over a significant period of time.
Today the word may also be used to describe a long and drawn-out story that is either written or spoken (as in “my neighbor told me the saga of his divorce again”).
Saga comes from an Old Norse word of the same spelling. It does not have any connection with the adjective sagacious (“possessing quick intellectual perceptions”), which comes from the Latin sagax (“sagacious”).