Rupin

Rupin is a character in Skyward Sword. He runs the Gear Shop in the Skyloft Bazaar, where he sells Link a variety of items, including shields, Deku Seeds, Bombs, Seed Satchels, Bomb Bags, Quivers, Arrows and more.

At night, he can be seen in his home in the residential district on the south-eastern part of Skyloft. In contrast to his assumed personality during the day, Rupin behaves rudely towards Link at night. He also will buy treasures at night, but only ones he chooses for that night.

If Link speaks with him at night,he will buy some treasures at the following prices:

Theory
It can be inferred that the Happy Mask Salesman is a decendent of Rupin, due to their career as shop owners and same facial expressions and mood swings.

Trivia

 * Rupin bears a similar personality and physical mannerisms to the Happy Mask Salesman.
 * Rupin's name is likely a play-on-words between the name "Rubin" and the word "rupee".