|Behind the scenes|
|First appearance||The Beginning|
|Last appearance||The Beginning|
|Cause||End of series|
The One was encountered by the Animorphs in the final book, The Beginning. It was believed by some fans that The One was first shown at the end of #41: The Familiar as the entity who put Jake in the fake future, because both have an interest in Jake. However, this speculation has been ruined by recent statements from K. A. Applegate. When asked directly whether or not The One was responsible for book 41, she responded by saying: "The One is a purely future creation/event, not entwined in the backstory."
The One somehow came into contact with several Yeerks who had been on the run from the Andalites, and The One promised them great power as long as the Yeerks worshipped it. To this end, it effectively turned them into a cult dedicated to worshipping The One. The One seemed to have the power to absorb or assimilate other beings, which is what it did to Ax, adding a mouth to Ax's face. At the end of the book, a ship belonging to The One was possibly destroyed when Jake gave the order to ram the Rachel into The One's Blade Ship (previously Visser Three's). It is not known what happened after that as the Animorph series ends with Jake giving that order.
It is theorized that The One is the entity that expelled Crayak from his galaxy millennia ago, and that The One is the single power greater than the Ellimist and Crayak, or that the One is another pawn of Crayak chosen to succeed the Yeerks in his "game" with the Ellimist. However, as The One has no official backstory, nothing about it can ever be confirmed. It is also possible that The One is an entity similar to the Drode, powerful but not on the level of Crayak or Ellimist.