A not very common character in the "The Legend of Zelda" series. She have made small appearances along the games, naver having big rolls ath the game plot. Her most recent appearance was at "The Legend of Zelda: Ocarina of the Time", as as usual, Princess Zelda's nanny/bodyguard.
Her race is defined for the first time in the same game. She is a Sheikah, an old and almost extinct race in Hyrule, the world (or region) where they live.
Man, I wish Impa had a bigger role... She never does anything important!