Aspect Co. Ltd (アスペクト株式会社 Asupekuto Kabushiki-gaisha) is a Japanese based video game company which was founded in March 1991. Aspect has developed for the Sega Master System, Game Gear, Pico, Genesis, Saturn, Super NES, Game Boy Advance, Nintendo DS, and WonderSwan Color. Aspect has also worked with the following companies; Sega, Takara Tomy, D3 Publisher, SquareSoft, Tec Toy, Banpresto, Takara, Disney Interactive Studios, and even Samsung. They are most well known for the development of every Sonic the Hedgehog game for the Sega Master System, Game Gear and Pico (minus the original Sonic the Hedgehog, which was developed by Ancient, and Tails' Skypatrol, which was developed by SIMS).
Source: Wikipedia, "Aspect Co., Ltd.," available under the CC-BY-SA License.