Harry is sneaky, wild, unpredictable (which can be perceived as crazy), rude, and evil but has a heart. His heart is shown (figuratively) when it comes to his hook. Harry is fond of his hook to the point of being obsessed with it. When Jay grabbed his hook and threatened to drop it into the ocean, Harry backed away and dropped his sword as people would do in a hostage situation. When Jay dropped it into the ocean, Harry jumped in after it without a second thought. The hook may be a memory or deep connection to his father, Captain Hook.
He considers Tourney to be "a wee boys game". Harry finds the idea of summer school laughable, as even the schools on the Isle did not have it; he laughs that it must be the reason Audrey snapped.
Harry has unquestioning loyalty to his best friend Uma, whom he immediately returns to obeying once they reunite in Descendants 3. After Uma, Harry is close to Gil, the muscle of their pirate crew; unlike the rest of their crew, the two of them stuck together during the two years Uma was gone from the Isle, always waiting for a chance to escape to find their leader and continue their pirating.
- Harry initially had a hard time accepting he was not the captain of the pirate crew, but by the time of Descendants 2, he shows an unquestionable loyalty to Uma and knows what she wants to be done. As her first mate and best friend, he follows her orders without any hesitation or complaint; as shown in What's My Name?, Harry even makes sure the rest of the crew knows to respect and obey Uma.
- Gil was seen kissing Harry Hook,  however, it was never scripted or directed and was an improvised scene between the two actors.  But it was mentioned in the novelization of the film Descendants 2.
- He is punctual (despite not knowing how to read a watch) and has a very violent imagination.
- He carries around a hook, resembling the one his father wore. However, he himself has two hands.
- In Rise of the Isle of the Lost: A Descendants Novel, some details about Harry are revealed:
- He is the second child of Captain Hook, while Harriet is the eldest and CJ is the youngest.
- He was the first one to join Uma's pirate crew.
- He once tried to entice Tick-Tock the Crocodile to bite his hand so that he could wear a real hook like his father, but the crocodile just opened one eye and went back to sleep.