How Gus the 'Lovable' Goldendoodle Went from Everyday Dog to the Star of “Lessons in Chemistry ”(Exclusive)

The Apple TV+ series' dog trainer Steve Berens and showrunner Lee Eisenberg tell PEOPLE that working with Gus, who plays Six-Thirty on the show, was a breeze

Rehearsing for a TV series is hard work for a human actor, but a dog's casting, training, and acting process is entirely different.

A Goldendoodle named Gus plays the role of Lessons In Chemistry's Six-Thirty. The curly-haired canine portrays a failed bomb detection dog on the AppleTV+ series — based on the bestselling book — who is rescued by chemists Elizabeth Zott (Brie Larson) and Calvin Evans (Lewis Pullman).

PEOPLE spoke to Steve Berens, a dog trainer on the set of the show, and Lee Eisenberg, the series' showrunner, about the experience of working with Gus.

It all started with the casting — though there weren't actual auditions for the role of Six-Thirty.

"While some projects require auditions, this one didn't work that way," Berens tells PEOPLE. "Originally, they wanted to cast a breed of dog that was uncommon, but it was going to be hard to find and difficult to train."

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That's when the series decided on a Goldendoodle for the role.

"I thought a Goldendoodle or goldendoodle would fit and was a dog I always wanted. So I started searching for a dog that could play the part of Six-Thirty," Berens says. "Gus was a private party dog looking for a new home. Once I spent a little time with him, I felt he would be a great dog to work with. I submitted his picture, and they loved his look."

After Six-Thirty's actor was secured, it was time to start training Gus for his big debut role. Rehearsals for dog actors aren't unlike rehearsals for human actors, particularly kids — canine stars need a lot of breaks, praise, and snacks.

"Typical prep days start with a walk. The day progresses with several short-duration training sessions. There are potty breaks, ball breaks, and play breaks in between," Berens adds. "The dogs love the attention and creative learning techniques."

"Usually, I will use other trainers as stand-ins for the actors, and we will act out the scenes," he adds. "I always like to try to get rehearsals with the actual actors. It helps the dog to build a rapport with the actors. I feel that both the actor's performance and the dog's performance benefit from rehearsal time together."

It didn't take too many rehearsal sessions for Gus to become the dog that "everyone really loved" on set, according to Eisenberg.

"Shooting with a dog is always a challenge, but Gus is incredibly lovable in person," he tells PEOPLE. "And I think that there's a buoyancy that comes to a set when there's a dog."

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"Louis, in particular, was so comfortable with dogs, and the two of them would go out on runs for the show, and they just immediately connected," the showrunner says of the bond that bloomed between Gus and Pullman.

"​​It's always a lot of fun watching a young dog gain confidence as you form a partnership performing the complexities and subtleties of a TV show," Eisenberg adds.

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Gus may have more acting parts in the future since he and his trainer are now roommates. When Berens selected the pooch for Lessons in Chemistry, he also adopted the Goldendoodle from private owners looking to give the dog a new home.

“I adopted him from someone who was rehoming him,” Berens says. “He lives with me.”

The first two episodes of Lessons In Chemistry will be available to stream on Apple TV+ on Oct. 13. Additional episodes will drop on Fridays through Nov. 24.

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