While it's generally agreed that the folkloric figures of "Link" and "Princess Zelda" are based on real historical individuals, neither those individuals nor their respective myth-cycles were contemporary, being separated in time by nearly two hundred years, with each initially being the protagonist of their own tales.
When the two myth-cycles were fused by later chroniclers to produce the combined Link-Zelda cycle which is familiar to audiences today, the figure of Link assumed the role of overall protagonist. Securing Zelda's freedom from captivity is often inserted as a secondary objective into episodes which were originally Link tales, while Link typically subsumes most or all of Zelda's role in episodes which were originally Zelda tales.
In many cases, the Link-Zelda version is the only iteration of a given episode which survives, so determining which tales were originally part of which precursor cycle is not without controversy; however, the repetitive nature of the perils which preclude Zelda's active participation in many episodes – kidnapped, possessed, sealed in enchanted crystal, etc. – may offer some clues.
(The Gamelon saga represents the the largest known body of Zelda tales which are believed to have persisted in more or less their original form. Linguistic analysis suggests that the episode in which Link is revealed to have been trapped in a heretofore-unmentioned magic mirror the entire time is a clumsy interpolation by a later author, inserted to justify the saga's inclusion in the broader Link-Zelda cycle.)
