What defines legend?
Etymology Online gives us the origin:
legend (n.) early 14c., "narrative dealing with a happening or an event," from Old French legende (12c., Modern French légende) and directly from Medieval Latin legenda"legend, story," literally "(things) to be read," on certain days in church, etc., from Latin legendus, neuter plural gerundive of legere "to read, gather, select".
Used originally of saints' lives; extended sense of "nonhistorical or mythical story" first recorded late 14c. Meaning "writing or inscription" (especially on a coin or medal) is from 1610s; on a map, illustration, etc., from 1903.
Merriam-Webster gives us a definition:
: a story from the past that is believed by many people but cannot be proved to be true
: a famous or important person who is known for doing something extremely well