Dr. Arewo Stein is a character who Wario encounters on multiple occasions while exploring the Golden Pyramid in Wario Land 4. He appears as a comically styled, elderly man with a large head, glasses, a mustache, and a beard. He is about 90 years old.
While his first and only appearance in a Wario Land series game was in Wario Land 4, Dr. Arewo Stein's character actually originated from Kaeru no Tame ni Kane wa Naru (カエルの為に鐘は鳴る, meaning For the Frog the Bell Tolls), a Game Boy game that was released exclusively in Japan. In said game, Dr. Arewo Stein is a member of the supporting cast surrounding the adventure of the Prince of Sablé. Dr. Arewo Stein works as a researcher for an institute on Nantendou Island, providing the protagonist with helpful items such as gloves that increase strength, or a device that can control mammoths. He also appears in the final battle of the game, riding a robot of his own creation, the Tokyo Comic Show Z, which assists in defeating the final boss. Dr. Arewo Stein is said to be a gourmet, and he frowns upon the thought of sharing his food. He is especially stingy when sushi is involved.
Source: The Game Website.