Estril 731
Biographical information



Unnamed Hork-Bajir




Aftran 942 (pool-sister)




Yeerk Empire

Behind the scenes
First appearance

The Departure

Last appearance

The Departure
The Sickness (mentioned)


Killed by Cassie

"Aftran had taken on the job to avoid having to kill. But her pool-brother, Estril, had stayed on as a Hork-Bajir. Estril had been acting as backup security to a meeting of The Sharing. A nothing job. No problem. Stay aboard a shielded ship, just in case... The "just in case" had been the battle. And I saw, with Aftran's memory, the image of a wolf, teeth bared in a vicious snarl... Me."

Estril 731, of the Hett Simplat pool, was a Yeerk assigned to reinforcement guard duty at a meeting of The Sharing.


"Humans can't morph. Only Andalites can morph. Only an Andalite could become a wolf and rip the throat from my brother's host body and leave him dying."
Aftran 942[src]

Estril 731 was the pool-brother of Aftran 942. While Aftran was assigned the human Karen as her host, Estril remained in a Hork-Bajir host body, assigned to general guard duty for the Yeerks during the invasion of Earth.

While serving as a reinforcement guard for a meeting of The Sharing, Estril was called into battle against the Animorphs, who had chosen to infiltrate the meeting. He fought against Cassie, in her wolf morph, and was killed by her.

Later, Cassie was briefly infested by Aftran, who accessed her memory of killing Estril. As she did, Cassie felt guilty about having killed him. It was this act of killing that had prompted her to leave the Animorphs for a short time.[1]


  1. The Departure