Hank is an octopus. Actually, he’s a ‘septopus:’ he lost a tentacle — along with his sense of humor — somewhere along the way. But Hank is just as competent as his eight-armed peers. An accomplished escape artist with camouflaging capabilities to boot, Hank is the first to greet Dory when she finds herself in the Marine Life Institute. But make no mistake: he’s not looking for a friend. Hank is after one thing — a ticket on a transport truck to a cozy Cleveland facility where he’ll be able to enjoy a peaceful life of solitude.
Hank first appears in the film in Dory's tank room in the Marine Life Institute, planning to escape into Quarantine so he can live a life of solitude in Cleveland. To do so, all he needs is a tag, which Dory has. He decides to help Dory find her family as long as she gives her tag in return.
Hank takes her through the building, but Dory sees a bucket labeled Destiny and causes herself to fall into a bucket of fish food for Destiny, a near-sighted whale shark, who tells her she's from the Open Ocean exhibit, and how to get there through the pipes. Dory decides not to go through the pipes and with Hank, as she thinks she'll get herself lost without company.
Dory and Hank use a baby stroller to find the Open Ocean Exhibit, but Dory's interest in the worlds most powerful glasses causes them to fall into a touching tank, where Hank shows his fear of being touched. Dory calms him down by telling him to keep swimming, only for him to release ink upon being poked, scaring all the kids away.
Dory and Hank finally make it to the Open Ocean Exhibit, where Dory thanks Hank for helping her by giving Hank her tag. Hank tells Dory he thinks she's ready before dumping her into the tank, but not before he tells her that he will have a hard time forgetting about her when Dory states that she thinks she'll remember him, finally revealing the softer, sweeter side of his personality.
Hank later appears in Quarantine and helps Dory, Marlin, and Nemo get to the Blue Tang tank, telling Dory to hurry as the truck leaves in 3 minutes. When Dory starts to hallucinate upon hearing her parents may be dead, Hank finally loses his patience and scoops Dory from the tank, leaving Marlin and Nemo in the tank by accident, only to drop the beaker carrying Dory when a human tries to grab him, sending Dory down a drain and back into the ocean where she finds her parents.
In the truck to Cleveland, Marlin and Nemo spot a fish they think is Dory, only for it to be a camouflaged Hank. He sadly apologizes for losing her as the doors close.
Dory, with the help of some otters, breaks into the truck and try to save Marlin and Nemo, only for Becky to appear and carry her bucket with Marlin and Nemo away, leaving Dory in the truck with Hank. Dory asks Hank to come live in the ocean with her; at first, he refuses but eventually accepts, possibly upon realizing that he'd rather be in the ocean with those he cares about instead of being in a glass box all alone.
Hank scares off the truck drivers and drives the truck around towards the ocean, only for it to fall off a cliff into the water, freeing all of the fish. At the end of the film, Hank becomes Mr. Ray's substitute teacher while the latter joins the stingray migration. When asked when Mr. Ray will return, Hank states that if Mr. Ray is smart, he would stay away from the class as long as possible.
During the credits, Hank hides in each scene throughout the film. He appears in certain scenes such as the kelp forest of Morro Bay on a pole, the quarantine area by the transport truck, the gift shop on a tank with a toy fish resembling Dory, the motorboat on the surface of Morro Bay where he controls it, the Open Ocean area on a "Wet Floor" sign, the tide pool exhibit where he hides in a large clam (the same clam that bothered Marlin and Nemo), the tree where Becky tries to land on but falls, the Open Ocean exhibit tank on a sunfish (the same fish that told Dory to be careful twice), the stingray migration where he blends in with the stingrays, the sunken beetle car where he hides inside and pretends to ride, and the midnight zone where he hides in a large crate with the giant squid inside it as he escapes from it.
Unlike real octopuses, Hank has only seven tentacles.
The real reason Hank only has seven tentacles is that the animators realized they were unable to fit eight onto his body. He was thus given seven, with the loss of his eighth tentacle being worked into his backstory, though it is never revealed exactly how he lost his tentacle. However, it is implied that he lost it in an incident that involved being touched by kids.
Strangely, all his arms are equally spaced and have surrounding webbing, and he does not seem to have a gap or a stump where his lost arm would have been (furthermore, octopuses can actually regrow lost arms, so his inability to regenerate his may imply severe trauma).
On April 1, 2016, Hank's voice actor, Ed O'Neill, was featured with Andrew Stanton as part of an April Fool's joke. The joke involved deceiving viewers into believing that Hank was the oldest and most coveted Pixar Easter Egg in history.
Hank is an octopus, and therefore he can survive out of water for some time, squirts ink when he's scared, and can change color for camouflage.
Hank's behavior is actually very similar to that of a real-life octopus: octopuses are notoriously hard to keep in captivity, as they are intelligent escape artists that are known to leave their tanks and wander around on land.
His camouflage ability not only has him changing color, but also his shape: a technique used by real-life octopuses (especially the mimic octopus) to escape predators or mimic more dangerous animals for defense.
Hank does not know that he, in fact, has three hearts (which is brought up by Dory) until he sees a sign near the Open Ocean exhibit that says so, which helped Dory remember where the exhibit was.
For some merchandise, Hank's mouth is seen on his body, which is incorrect as it is under him.