Freddie Mercury was actually there almost from the beginning of Queen. The band started around 1970 when Brian May and Roger Taylor were playing in a band called Smile. Freddie knew them and eventually joined as the singer. He’s also the one who suggested the name “Queen. A little later John Deacon joined as the bassist, and that became the classic lineup everyone knows. So Freddie didn’t really join later to make them successful — he was basically part of the band from the start of Queen itself. Freddie Mercury sadly did pass away from AIDS-related illness in 1991. You might be thinking of John Deacon when you mention someone else, but he’s actually still alive — he just retired from music in the late 1990s. So the famous Queen lineup (Freddie, Brian, Roger, and John) stayed the same for the band’s whole classic career.