From Wikipedia
Intelligent Systems Co., Ltd. (株式会社インテリジェントシステムズ, Kabushiki-Gaisha Interijento Shisutemuzu?) is a Japanese first-party video game developer and internal team of Nintendo Co., Ltd.
Intelligent Systems entered the video game industry as a one-man team, named Toru Narihiro, who was hired by Nintendo to port over Famicom Disk software into the standard ROM-cartridge format that was being used by the NES outside Japan. The team soon became an auxiliary program unit for Nintendo (like HAL Laboratory originally) that provided system tools and hired guns to program, fix, or port Nintendo-developed software. Thus much of the team's original discography contains minuscule contributions to several big Nintendo R&D1 and Nintendo R&D4 titles.
Chief programmer Toru Narihiro programmed his first actual game software with Famicom Wars and Fire Emblem towards the end of the Famicom's life cycle, although the game design, graphic design, and music was provided by the Nintendo R&D1 team. But because of Narihiro's success, Intelligent Systems began to hire graphic designers, programmers, and even musicians to extend the company from an auxiliary–tool developer to an actual game development group.
Intelligent Systems currently focuses on DS and Wii development, and has developed games for all of Nintendo's previous handhelds and consoles.