suffix, noun
Used as a suffix attached to a noun to form a compound meaning 'story of ...' or 'tale of ...', as in 英雄譚 (heroic tale). Also used as a standalone noun in literary contexts.
See also: 英雄譚 (えいゆうたん)
この小説は、ある探検家の冒険譚だ。
This novel is the adventure tale of an explorer.
彼は古代の英雄譚を集めて本にした。
He collected ancient heroic tales and made them into a book.
物語 is a common, general word for 'story' or 'tale', while 譚 is a more literary suffix/noun often used in compounds to specify the type of story.
The kanji 譚 is used for its meaning 'story' or 'tale'. The reading たん is the on'yomi. The exact historical derivation of this suffix usage is uncertain, but it is conventionally associated with literary or narrative contexts.