- "Polar bear. The largest land predator in the world."
- "Rachel wrapped her own big paws around him and together we wrestled Hulk Frozen to the ice. Tobias swooped down out of the sky, complaining about there being no lift at all in this cold air. Like that was the major drama. He sank talons into Derek's friend Nanook and began to acquire him, while Rachel and I lay panting and counting our wounds. The bear went into the acquiring trance and a few minutes later we all had his DNA floating around inside us."
The Animorphs acquire their polar bear morphs in The Extreme. While struggling in the North Pole as they lacked Arctic morphs of any kind, the Animorphs encountered Nanook, a polar bear, with Marco suggesting they acquire him. Shortly after, they meet Derek, a jocular Inuit who states that Nanook is his friend. Marco asks Derek to take them to Nanook so that they may acquire him. Rachel and Marco morph into their grizzly bear and gorilla morphs and tackle Nanook, beating him into submission. While restraining him, Tobias swoops down and acquires him, placing Nanook in the acquiring trance. Jake and Cassie then acquire him as well, extending the trance while Marco and Rachel demorph and acquire him as well, running away before the trance could fade. Sometime between The Ultimate and The Answer, one of Tom's Yeerk's followers acquired a polar bear morph, most likely from The Gardens.
Stranded in the Arctic
- "We had the morph for this place. Like being a tiger in the jungle or a crocodile in a swamp, we owned this place now. Owned it! I've been a gorilla. I've been a rhinoceros. I've felt power before. But this was new. [...] We sauntered back toward the Yeerk base with the cockiness of Clint Eastwood going into the town saloon. It was a long walk, punctuated by refreshing plunges into the icy water. We ended up having to demorph, of course, and that was no fun at all. But then it was back to being Lords of the Ice."
As the largest land predator on Earth, the polar bear was considered to be perfect morph for the Animorphs to use while being stranded in the North Pole. Possessing raw power and sheer strength, the polar bear is the Animorphs' most powerful morph. The Animorphs used this in The Extreme to traverse the Arctic environment and to infiltrate the Yeerks' base.
Used by Cassie
Cassie morphed the polar bear in Elfangor's Secret in order to become "white" after a racist man confronted her for being black. She later used it as a battle morph in VISSER to stage an attack against Visser Three in the presence of the Council of Thirteen at Visser One's bequest. After being captured by the Yeerks in polar bear morph in The Weakness, Cassie partially demorphed to escape her shackles and promptly remorphed, using the morph to fight Hork-Bajir-Controllers. Cassie relied on the polar bear morph as her battle morph in The Unexpected, in order to fight off two Hork-Bajir-Controllers in the cargo hold of an airplane headed towards Sydney, Australia.
Attack on The Sharing's Community Center
- "If you guys are really that worried, we'll go in with maximum firepower. We all go in as polar bears!"
"Did I hear you correctly? 'Cause I don't see anything wrong with our usual battle morphs."
"He's got a point, Rachel. We know our morphs. They've been working for us all day. We handle them best."
"We're going for mass here, people. Bulk. Spectacle. Going out in style. Besides, we want to send the message that there are a lot of us."
- ―Rachel, Marco and Cassie
The Animorphs, minus Jake, used the polar bear as an alternate battle morph under Rachel's leadership in The Weakness, since the polar bear was the strongest morph they possessed. However, they discovered the hard way that the polar bear became sluggish at high temperatures and was not a suitable morph for their hometown environment; additionally, Ax remarked that they had no versatility or flexibility in the same morph and thus they all struggle from the same weaknesses. Following this instance, the Animorphs reverted back to their original preferred battle morphs.
To be added
- The Stranger (mentioned and seen at The Gardens)
- The Extreme (Nanook; acquired and morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- Elfangor's Secret (morphed by Cassie)
- The Prophecy (mentioned)
- The Proposal (poodle–polar bear hybrid; morphed by Marco)
- VISSER (morphed by Cassie)
- The Weakness (morphed by Rachel, Tobias, Cassie, Marco and Ax)
- The Other (mentioned)
- The Unexpected (morphed by Cassie)
- The Sacrifice (morphed by a human-Controller)
- The Beginning (morphed by a human-Controller/Rachel's killer)