Professor

Dr. Mizumi is a scientist who lives in Lakeside Laboratory located near Lake Hylia. He is simply referred to as "the crazy old man", as he was not named in the games.

In Ocarina of Time, he is a chemistry scientist, and makes medicines at his Laboratory. It is stated that he loves the taste of Eyeball Frogs. In Majora's Mask, he works at the Marine Research Laboratory as a marine scientist. He worries about the pollution in the sea, and takes care of Lulu's eggs until they hatch.

Dr. Mizumi is of an unknown race. Link encounters a nearly drowned Rouru in a lake, and decides to bring him to Dr. Mizumi. Mizumi offers to let Rouru stay at his laboratory until he recovers. Soon after, though, Rouru has a fit and destoys most of the doctor's experiments and equipment. After Rouru is healed, he leaves with the rest of his flock and Link offers to help rebuild Mizumi's life work.

Dr. Mizumi's Terminan counterpart appears in the Majora's Mask Manga as a fisherman. He mistakes Link for the Zora, Mikau, since he is wearing the respective mask. Link gives him Lulu's egg for safe keeping and study.

Trivia
Dr. Mizumi's name is spelled with two "U'"s (Mizuumi) in the Majora's Mask Manga.