Humpback whales (also known as the "great ones") are sentient lifeforms who can communicate among both themselves and other sea creatures, such as bottlenose dolphins, using a form of telepathy. The Animorphs first encountered one in The Message, where it told them where the Andalite Dome ship was after the Animorphs rescued it from sharks, after which it helped keep a drowning Marco afloat as gratitude. Later on, the whale and its allies save the Animorphs from being killed by Visser Three in his mardrut morph, and towed the Animorphs and Ax back to shore.
- "I pressed my human hands against the side of the whale. I focused my mind on the process of "acquiring." It felt... wrong, somehow. As if I should have asked the whale's permission. But the slow, vague communication of whales does not allow for explanations. I needed his DNA. He slowed and almost stopped. It was the acquiring trance. All animals become calm while they are being acquired. But it was hard to think of the whale as being just an animal. I had dealt with whales before. They are not intelligent in the same way humans are, but they have minds, and, I believe, souls. When I was done acquiring the great one's DNA, I took my hands from him."
In The Andalite's Gift, Tobias locates a humpback whale as a request from Cassie, who acquired and morphed the whale in order to kill the Veleek, a morph-hunter. Aftran 942 acquires a humpback whale in The Sickness, trapping herself in morph.
Cassie uses the humpback whale morph for the first time in The Andalite's Gift, after discovering that the Veleek could not lift Rachel in her African elephant morph and that it did not like water. After ensuring that the Veleek caught her, Cassie morphed into the whale, dragging it into the water, where it was dispersed and killed. Cassie used the morph again in The Solution, when David was using his orca morph to kill the Animorphs, who were in bottlenose dolphin morph. Despite the fact that orca have teeth and humpbacks do not, David's lack of knowledge and the fact that humpbacks were much larger in size forced David to flee. After being shrunk by the Helmacrons in The Suspicion, Cassie made her way to the top of the Helmacron ship and used her humpback whale's mass to weigh down the ship. Cassie went on to use the morph in The Conspiracy to destroy a lakeside dock that Tom and his father were on and used the morph once again in The Prophecy during a trip to the Hork-Bajir homeworld, combining the morph with her osprey morph to create a winged humpback whale, which she used to invade the Yeerk pool, with the other Animorphs in battle morphs hiding in her massive whale mouth. During a journey into Marco's nose, Cassie used the humpback whale morph to ferry Rachel, Jake, Tobias and Ax across his stomach acid.
- "There were five of them in the water. The two big males who had struck first had heads like sledgehammers. Sperm whales. Sixty feet long. Sixty-five tons. The weight of fifty cars. They had dived deep and come tearing up at awesome velocity to slam into the creature from another world's ocean. The mardrut was big. The mardrut was strong. But nothing living can survive for long, being slammed by creatures weighing a hundred and thirty thousand pounds."
In The Exposed, the Drode causes a sperm whale to beach in order to give the Animorphs a chance to acquire it. However, The Sharing and other beachgoers surround the whale in an attempt to free it, making it extremely difficult for all the Animorphs to acquire it, and impossible for Ax since he cannot be in his Andalite form in public. Jake makes the decision that only two of them will acquire it, which end up being Rachel and Tobias. While acquiring the whale, Tobias is spotted by Chapman and Tom and gets his talons stuck, forcing the other Animorphs, in seagull morph, to free him.
Rachel and Tobias used their sperm whale morphs in order to find a giant squid for the Animorphs to collectively acquire, since it was one of the few creatures capable of diving deep enough to access the Pemalite ship. The pair morph sperm whales once again in The Mutation, after using their orca morphs to damage the Sea Blade in the ocean.
The Animorphs encounter what they believe is a wild orca in The Solution, only for it to be David in morph. They later encounter two wild orca while stranded in the North Pole in The Extreme, chasing after them since the Animorphs are in baby seal morphs. In The Mutation, The Gardens received an orca named Swoosh in The Mutation; it also featured two wild orca that the Animorphs encounter in the ocean.
- "Whales are good. We need a morph we can control. Something intelligent. That can dive deep and do some serious damage to the Sea Blade. But let's face it. The chances of another sperm whale beaching itself just for the rest of us to acquire are pretty slim."
"Of course! There's an orca – a killer whale – at The Gardens' SeaTown. They're calling him Swoosh."
- ―Jake and Cassie
David is the first Animorph to use the orca morph, utilizing it in The Solution as an attempt to kill the other Animorphs while they are in their dolphin morphs. He nearly succeeds, but is driven off by Cassie, who uses her humpback whale morph's sheer size to scare David away. In The Mutation, Jake, Rachel, Tobias, Cassie, Marco and Ax morph orcas in order to follow the Sea Blade into the ocean and use the orca's weight to ram the Sea Blade, in an attempt to destroy it before the Yeerks could use it to locate the Pemalite ship.
- The Message (humpback whales, sperm whales)
- The Andalite's Gift (humpback whale; acquired and morphed by Cassie)
- The Change (humpback whale; mentioned)
- The Escape (mentioned)
- The Warning (mentioned)
- In the Time of Dinosaurs (mentioned)
- The Solution (orca, acquired and morphed by David/humpback whale, morphed by Cassie)
- The Suspicion (humpback whale, morphed by Cassie)
- The Extreme (orca)
- The Exposed (sperm whale; acquired and morphed by Rachel and Tobias)
- The Sickness (humpback whale, acquired and morphed by Aftran 942; becomes trapped in morph)
- The Conspiracy (humpback whale, morphed by Cassie)
- The Separation (mentioned)
- The Prophecy (humpback whale, morphed by Cassie)
- The Mutation (orca; acquired and morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax/sperm whale, morphed by Rachel and Tobias)
- The Hidden (humpback whale, partially morphed by Cassie)
- Back to Before (mentioned)
- The Journey (humpback whale, morphed by Cassie)