Elvis Presley pictured singing in what most fans call his comeback, 1978's Grease. In the movie, he appears as Frenchy's guardian "Teen Angel" who gives her a reality check on the situation she was in, just like he gave himself back in 1976.
He had been asked to star with Barbara Streisand in A Star Is Born, he had expressed interest in joining the film, but his manager at the time Colonel Tom Parker, asked for a substantial amount of money and top billing for him, which they obviously passed on. This greatly angered Elvis, as his manager had just made him pass on what could've been a great comeback movie for him.
One day he marched into the Colonel's office with a team of lawyers and told him he was fired, the Colonel obviously protested, and threatened to take legal action against him, which Elvis was already ready for. So he brought his status as an illegal immigrant up, which he can use against him. He stepped down, and was fired.
He later killed himself in a dingy trailer outside of Las Vegas in 1979, leaving millions owed in gambling debts.
Elvis however, had just gotten the comeback he wanted, albiet not what he expected. Throughout the last couple of years he had been losing weight, working on his drug addictions, and really just working on himself. But in 1978, he had been asked by Robert Stigward to make a cameo in a movie that he was working on... Grease. This was just the movie for him, and not so long later, he had filmed the scene, recorded the song, and now was waiting for the release.
When it was released, it was a triumph for him, introducing him to a new generation of fans. He had to somehow make this success worth something, so he kept on working, cameoing in another movie the Blues Brothers, where he played a pentecostal preacher, who was had a singing duel with other preacher just across the street, played by James Brown. He was also amused to see that his song Jailhouse Rock was used in the ending of the film.
During 1980, Queen frontman Freddie Mercury gifted him a song, a song which would become his most successful single in years.