Danny is portrayed by John Travolta in the 1978 film, by Aaron Tveit in the 2016 live performance.
Danny is an 18 year old handsome older teenage boy, with thick black hair with a lot of hair grease and blue eyes and walks with a swagger. He's mostly seen wearing a t-shirt tucked into black jeans with a black belt, and black penny loafers with white or black socks. Danny's hair is done up in an DA (ducks ass) - a popular `greaser' style of the 1950s - and he's almost always seen with his black leather jacket with the T-Birds logo on the back, the only exception being towards the end of the movie, at the carnival, when he earned his letterman sweater in track, and wore it in order to impress Sandy, in turn shocking his fellow T-Birds, as the rest of the school. He went back to his T-Bird jacket when Sandy showed him her new "female greaser" look.
During summer vacation at the beach, he meets and falls deeply in love with Sandy, a beautiful and sweet girl from Australia. When it's time for her to return home to Australia, he believes their relationship is only the beginning, but he doesn't expect to see her again.
When the new school year starts, unbeknownst to Danny, Sandy's parents decide to move to America and become Americans, and Sandy enrolls at Rydell High School, and Frenchy befriends her. After Sandy tells the Pink Ladies that she met Danny at the beach during summer vacation, Rizzo arranges for them to be reunited. Danny was shocked see Sandy again, but he was under pressure from his fellow T-Birds to act cool. Danny acts crude and rude, breaking Sandy's heart. She called him "a fake and a phony" and ran away crying. The T-Birds are scornful of Danny’s loving relationship with Sandy, feeling it made him look soft. Keneckie especially did not like Sandy, as he was secretly in love with Danny. Upset, Danny shows up outside of Frenchy's house with the T-Birds in Kenickie's new car, but gets out of the car and leaves. A few days later, Danny sees Sandy spending time with Tom Chisum, one of the jocks. He tries to apologize to Sandy by trying to explain his situation with the T-Birds, including saying that "it was him, but it wasn't him," and Sandy describes Tom as "a simple person." Danny denies that he's jealous, and after learning that Sandy liked jocks, he decides to become one himself. He eventually becomes a runner, determined to do anything to win her heart and be with her again. When Danny falls trying to jump over a hurdle, Sandy tries to talk to him, and they decide to reunite. They try going out on a date, but their friends crash the date.
Danny takes Sandy to the school dance. Unfortunately, Sonny grabs Sandy and takes her away from Danny, and Cha Cha grabs Danny's arm and gets him to dance with her so they could win the dance contest. Sandy is devastated and leaves. A few days later, Danny tries to make it up to Sandy by taking her to a drive-in movie. He gives her his ring, but then tries to make out with her in his car. Sandy fights back, getting out of the car and throwing Danny's ring in his face and runs off. Danny is heartbroken, believing the two of them belong together.
The T-Birds and their rivals get together for a car race. After Kenickie bangs his head on his car door, Danny drives the car instead. Sandy watches the race and is thrilled when Danny won. Afterward, she tells Frenchy she isn't happy, but thought she knew a way she could be, and asks Frenchy to help her.
At the school carnival, Danny shows up wearing a letterman sweater in track, and tells his fellow T-Birds that they and Sandy mean a lot to him. Sandy shows up dressed like a "female greaser" and shocks everyone - especially Danny. They pledge their love for each other, and drive away together in a Greased Lightning Car.