Animorphs is a book series created by K.A Applegate, with 54 main books, as well as four "Chronicles", detailing the past - and often the struggles - of the various alien species peripherally involved in the struggle. It tells the story of five - later six - teenagers, and their struggle to prevent the Earth from being conquered by a race of parisites called Yeerks.
Not all is as it seems, however, and the Animorphs soon come to realize that their battle has a greater significance than they had known at first.
Characters in Canon
Yeerks and Controllers
Jeremy Jason McCole
The Council of Thirteen
Aliens of the series
A crossover between the universes of Animorphs and Teknoman, involving a covert Radam effort to conquer Earth, and spanning three stories thus far. The Animorphs are joined by Slade and Shara, both of whom have been transformed into Teknomen by the Radam.