The LEGO Bionicle theme was introduced in 2001.
Bionicle was a major LEGO experiment in story-led construction figures. Instead of relying mainly on conventional System bricks, its early action figures used Technic-style beams, ball joints, masks and specialised connectors. The first central heroes were the six Toa Mata: Tahu, Kopaka, Lewa, Pohatu, Onua and Gali, each associated with an elemental power.
The launch was supported by an unusually extensive fictional universe. Comics, books, games, online material and later films expanded the story of the island of Mata Nui and its biomechanical inhabitants. That multimedia approach helped Bionicle stand apart from ordinary LEGO play themes and built a particularly devoted fan community.
The year 2003 is an easy mistake because it marks the release of Bionicle: Mask of Light, one of the best-known films in the franchise. The original theme continued through several story arcs before its first run ended in 2010.