River Devil

The River Devil is a black, tree-like creature that blocks the single north-south road of Eastern Hyrule in The Adventure of Link. Though citizens of Nabooru speak of him in fear, he does not attack, and serves merely as an obstruction. The only way to pass him is to play the Flute found in the Palace on the Sea.

Trivia
The River Devil has a much more mammalian appearance in the Japanese version, being bipedal and having brown skin. It is unclear as to why the sprite was changed.