Navi the fairy made her big debut in one of the best video games ever, The Legend of Zelda: Ocarina of Time. Supplying Link with information, from where to go next to how to defeat his enemies, Navi guided him through his journey 'till the bittersweet end. Even when being onslaughted by enemies, she never left Link's side and was always there to point him in the right direction. So I'm proud to present... Navi!!
While it's unknown when Navi was born, it's safe to assume that she has resided in Kokiri Forest for most of her life and was on friendly terms with the Great Deku Tree. This is evident as he called her by name to assist Link on his journey. This also shows that she did not have a Kokiri child of her own to look after, and therefore was not restricted to stay in Kokiri Forest.
Navi is very smart, as she not only knows the name of most of the monsters that Link encounters, but also their weakness. This shows that she either traveled outside the forest or listened to many stories from the Great Deku Tree. Perhaps both?
Personality wise, Navi is rather energetic, and is very straightforward in a polite kind of way. She is quick to speak her mind, and often has wise advice on what Link should try to do next. However, because of her straight-forwardness, she often comes off as bossy or annoying. But you have to understand that from the moment Navi joins up with Link, all hell is breaking loose! Their guardian spirit and mentor, the Great Deku Tree, had just died from a curse that Ganondorf had placed in him, and the rest of Hyrule was facing Ganondorf's wrath. There was no time to mess around! Link had to help Hyrule to the best of his ability, and he had to do it now.
And Navi helped him do this with her special skillz. They include:
Navi really is a sweet fairy, and clearly cares for Link. But where she went to after she left Link when he completed his destiny, is a complete mystery. Why she left too, is unknown as well. I suppose she departed from Link because he no longer "needed" her. I mean, he saved Hyrule; his mission was complete as was hers to guide him. But where she went to no one knows, and that's where Majora's Mask picks up. Link clearly grew attached to the blue fairy, otherwise he wouldn't have gone deep into the Lost Woods in order to find his "beloved and invaluable friend, with whom he parted ways with when he finally fulfilled his heroic destiny". And if you say he was looking for the Skullkid, I swear to God, I'll slap you.
...However, Link never found Navi on his journey in Termina, and one can only assume that he continued his search when he made it back to Hyrule. But where did Navi go? Perhaps she went on her own personal journey, to discover herself or look for new people to help. Or maybe, tired from all the adventuring, returned to her home or some Fairy Fountain to rest her spirit. Either way, she'll always be remembered as the fairy who guided the Hero of Time.
* Measurements are estimated.