Minifigures built from special, uniquely molded pieces were first introduced in Life on Mars. Martians are composed of five tools: two pairs of double arms, a mechanical torso, a conjoined leg piece, and a head. This configuration is also used for many Star Wars Droids; Battle Droids follow the same pattern, while Super Battle Droids feature a head fixed to a torso, General Grievous has space for four arms, and IG-88 has a head constructed of other Lego pieces. Other droids, such as Droidekas, Spider Droids and Pit Droids, are constructed entirely from standard Lego pieces, yet are still generally considered minifigures. R2-D2 and other astromech droids are constructed from unique parts, with a separate top, body and legs. The robots of Exo-Force, Mars Mission commander aliens and Bionicle miniatures have a design similar to the Star Wars Battle Droids, but with separate legs, movable hands, and a head affixed to a small torso. Hagrid, the half-giant character from the Harry Potter series, uses a larger minifigure body, with only the head being separable.