Who sang the theme song in the movie “Grease”? in Wikipedia

1.  Frankie Valli
Frankie Valli (born Francesco Stephen Castelluccio; May 3, 1934) is an American singer and actor, known as the frontman of The Four Seasons beginning in…
https://en.wikipedia.org/wiki/Frankie Valli

2.  List of number-one singles in Australia during the 1970s
Garrett, "Emotion" by Samantha Sang, "Ebony Eyes" by Bob Welch, "Warm Ride" by Graham Bonnett, "Grease" by Frankie Valli, "Hopelessly Devoted to You" by…
https://en.wikipedia.org/wiki/List of number-one singles in Australia during the 1970s

3.  Clay Aiken
"Reviews: From the chilling future of ‘Marjorie Prime’ to the nostalgia of ‘Grease‘". "American Idol alum Clay Aiken dazzles in Pittsburgh CLO’s Grease". Rogers…
https://en.wikipedia.org/wiki/Clay Aiken

4.  List of baritones in non-classical music
releasing 90s shoegaze, hosting show in Brooklyn with Blouse & more". BrooklynVegan. Retrieved 6 June 2019. "Frankie Valli & The Four Seasons". WLHH. Retrieved…
https://en.wikipedia.org/wiki/List of baritones in non-classical music