"The mysterious mastermind of the tank gang, moorish idol fish Gill hides a kind heart under his moody exterior. He believes that fish were not meant to live in a box, and dreams of freedom. Gill has a genius for inventing crazy escape plans, but so far none have ever succeeded. Not even the one where everyone gets to roll over the window in plastic bags..."
Gill's only dream is to escape from the tank. He had made several escape attempts, but the first time, he landed on dental tools, giving him severe scars on his right side, and destroying his right fin. His appearance is modeled after the voice actor who does his voice, especially the coloring around his mouth to show the deep wrinkles that Dafoe has on his face.
Unlike the other Tank Gang members, Gill had a neutral reaction to Nemo's entrance. He also told Nemo to swim out of the tube he was stuck in without anyone's help. Learning that because Nemo is a young boy who can fit through small tubes, Gill immediately put together a plan to have him use a pebble to stop the aquarium filter. With the filter sabotaged, he knew the dentist will put the fish in bags and they will have the opportunity to return to the ocean.
Eventually, Gill helps Nemo escape the office by jumping onto the dentist's mirror to catapult the clownfish into the air so that he lands into a sink leading to a drain, which leads to the ocean. After Dr. Sherman puts Gill back into the tank, the Tank Gang congratulates him on finally succeeding in helping Nemo return to the ocean.
At the end of the film, Gill and the other Tank Gang members manage to escape from Dr. Sherman's office. Since Dr. Sherman's new AquaScum 2003 has broken (presumably sabotaged by the fish), he has to take his fish out, put them in bags, and clean the tank himself. While he complains to his secretary Barbara about the device breaking when it has a lifetime guarantee, Gill and the others make their way out of the office. They are seen having crossed the street and jumped into the ocean to their freedom.
In Finding Dory, Gill, along with the rest of the Tank Gang, appears in the post-credits scene. They are still trapped in their respective bags, now covered with algae. Gill congratulates the gang and proclaims that they will not have any more problems, shortly before they are captured by the Marine Life Institute volunteers.
- Gill's voice, as Dafoe said, is based on the character Earl Copen, whom he plays in the movie Animal Factory.
- His mannerisms are quite similar to Doc Hudson from Cars.
- Gill's species, Moorish Idols, are notoriously difficult to keep in captivity due to their diet and mannerisms. This may be an interesting way to show Gill's deep desire for escape from the aquarium and into the ocean. In addition, Gill was pressuring Nemo to follow his challenging orders on his escape plan.
- Gill may have been acquainted with Marlin in the past, as his final words to Nemo before flinging him into the spit-sink were: "Tell your dad I said 'hi.'"
- His Polish name is "Idol" (from his species) because Gil means "bullfinch" or "mucus" in Polish.
- Together with Nemo, Gill is the only member from the "Tank Gang" who is not bought from a store but is from the ocean.
- In "Finding Nemo", Gill stated that he never knew his parents.