Gus

"I already know Ruby. I want the chance to meet Red."

Gus was a domestic mouse who lived in the pantry of Cinderella's house. When the Dark Curse was enacted, Gus was trapped in Storybrooke, Maine, in human form, as Billy, the local tow truck driver, who had a soft spot for Ruby. Eventually he was gruesomely murdered as part of a revenge ploy put into motion by one of the town's most loathsome residents.

Before the Curse
"I was a mouse. My name was Gus. I lived in Cinderella's pantry, I ate cheese and gnawed on wood, but I preferred the cheese..."

Gus was a mouse who lived in the pantry of Cinderella's house, eating cheese and gnawing on wood. Eventually, Queen Regina enacted a curse with the sole intent of ripping the inhabitants of that land to another one where all their happy endings would be taken from them, including Gus the mouse.

Season 1
"Be careful! You almost shattered my wolf thing, Billy. It's good luck."

- Ruby

Front view of Granny's Diner, in Storybrooke, Maine. Billy, the tow truck driver, is seen lowering Ruby's car in front of the establishment, while Emma, accompanied by Henry, questions the waitress about Ashley's whereabouts. She asks him if she thinks Ashley's boyfriend was involved in her disappearance, to which Ruby, who is tending to some customers, tells the blonde that that would mean he was involved with her at all, which he isn't. She adds that Sean left Ashley in the lurch right after they found out she was expecting, and hasn't spoken to her since. Ruby starts to say something else, but she is interrupted when the hoist that's holding her car in the air abruptly drops the vehicle on the road. Ruby calls out for Billy's attention, telling him to be careful, for her almost shattered the red wolf pendulum hanging from her front visor, which she claims to be for good luck. Billy apologizes and points out that the wolf ornament is fine, and Ruby gives the tow truck driver a flirtatious look.

When the local mines collapse and are sealed shut with Henry Mills and Dr. Hopper trapped inside, a rescue team starts working on attempting to salvage them, including Billy, the tow truck driver. When Emma uses Pongo, Archie's dog, to try and get a sense of where his owner might be, Pongo leads them to an air shaft that leads to the tunnels. Ruby, driving Billy's truck, is able to remove the grade from the air shaft, and Emma is then lowered into it by Billy's hoist, eventually being able to rescue both of the mines' captives. Later, Billy and Ruby commemorate by having a beer together.

After Ruby finds Kathryn Nolan alive, her friend Mary Margaret is acquitted from the ongoing accusations against her, and thus the townspeople throw her a "welcome home" party to commemorate her innocence, and Ruby is in attendance, along with Billy and Granny, and many others. Mary Margaret wonders why all these people came to welcome her home, to which Emma comments that she has a lot of friends... and the teacher is forced to reply that it didn't seem that way the day before. When Henry gives her a card from his entire class, Ruby smiles.

Season 2
"He was better than you'll ever be."

- Red Riding Hood

Billy meets Ruby at Granny's Diner and tells her of his past, in fairytale land, as a mouse named Gus, who lived in Cinderella's pantry. Billy offers to buy Ruby a drink that night, hoping to get to know her better now that the curse has been lifted and they remember their pasts. However, Ruby seems reluctant to agree, and then her new friend Belle steps in, having noticed she wasn't comfortable, and tells Billy that they already have a girls' night planned. Belle then tells Ruby that Billy seems nice, but Red is still a bit wary. It is later revealed that it's because that night will be the first night of full moon since the curse was broken, and Red worries about reverting back to her wolf form and not being able to control it. That night, her fear comes true. And come the morning, they are horrified to find that Billy has been murdered, and cut in two. Red thinks that it was her who did it, but David is convinced it wasn't. They then discover that it was really King George, who killed Billy so that he could pin the murder on Red's wolf form and prove to the town that David wasn't a fit leader, for protecting a murderous creature.

Origins
The character of Billy/Gus is based on the eponymoys mouse featured in the 1950 film adaptation by Disney of the famed fairytale, "Cinderella" (also known as "The Little Glass Slipper"). Thousands of variants are known throughout the world of this folk tale embodying a myth-element of unjust oppression/triumphant reward. The story was first published by French author Charles Perrault in 1697. In the film, Gus (whose real name is Octavius) is a new mouse who appears in Cinderella's house and is welcomed into the pre-existing mouse clique, and given his nickname and petite clothing to wear. Gus serves as one of the mice sidekicks, helping Cinderella through the dramatic twists and turns that eventually lead her to go to the royal ball and fall in love with the prince. The general story of Cinderella consists of the character being unfairly treated as a servant by her evil and unappealing step-family, only to be granted the wish of going to a prince's ball by her fairy godmother, eventually marrying him and living happily ever after. An important detail of the story is the pair of glass slippers that Cinderella is given to wear by her fairy godmother, of which she loses one when rushing home from the ball at midnight. The prince uses said shoe to track her down, and when Cinderella's foot fits, he knows he's found the girl he met at the ball and fell in love with.