Frustrated with his inability to take a more aggressive stance in the conflict, he convinced the Animorphs to steal the Pemalite Crystal from the Yeerks and used it to reprogram himself for fighting. After taking down ten Earthlings and two dozen Hork-Bajir, not to mention reattaching Ax’s severed arm, he was wounded by the eternal memory of battle and changed his mind. Now he merely helps by espionage.
He has infiltrated the Yeerk society by accepting infestation, but with his robotic mind he was able to reverse the Controller process and take power over his would-be host. Erek kept the Yeerk alive with his own homemade Kandrona rays, and whenever visiting the Yeerk pool he created holograms of it going in and out of the pool. His inside information has always been very helpful to the Animorphs.