The Hork-Bajir Chronicles

Dak Hamee is a unique Hork-Bajir. His people call him a seer. He learns more quickly and completely than the rest of his docile race. Hork-Bajir like him are born once a generation.
Aldrea is a young Andalite. Daughter of the notorious Prince Seerow. It is only after she and her family are sent to the Hork-Bajir home world that she begins to fight the Yeerks — and, with Dak’s help, ultimately discovers their hideous plan.
Esplin 9466 is the Yeerk that will become the feared Visser Three. He has set out to defeat the Hork-Bajir, and begin the building of the Yeerk Empire.
This story chronicles the fierce Hork-Bajir wars in a time before the Animorphs.