Saria was Link's childhood friend in The Legend of Zelda: Ocarina of Time.
Right before Link started his quest to save Hyrule, Saria greeted him near the exit. She presented to him his first ocarina in a very emotional scene fans cherish to this day.
In the future Hyrule, Saria had gone missing in the Lost Woods. Link managed to find the forest temple deep within the woods, and defeated Phantom Ganon. After that, Saria arrives and gives Link the forest medallion.
She then gets promoted to Forest Sage, and help seal away Ganon after his defeat.
After that, she doesn't make many appearances in other games. Except her own stained-glass artwork in The Wind Waker.
And of course her graphical upgrade in The Legend of Zelda: Ocarina of Time 3D.