Saria is a member of the eternally youthful Kokiri race, and resides along with her kin in their provenance, the Kokiri Forest. Appearing jubilant and pleasant-mannered, she is popular among her people and is also the lifelong friend* of Link. Saria is willing to do whatever she can to help Link in his quest, and often lends her advice to him via their shared connection through their Ocarinas.

As quoted from The Great Hyrule Encyclopedia:

Saria was one of Link's first and closest friends. She was an elfin child of the Kokiri Forest, and unlike the other children, she refused to make fun of Link for being an outsider and not having a guardian fairy. Later, Link learned that Saria was in fact the Sage to the Forest Temple, holder of the Forest Medallion.