ABBA were formed in Sweden and were comprised of Benny Andersson, Björn Ulvaeus,  Agnetha Fältskog and Anni-Frid “Frida” Lyngstad. Benny and Björn had started writing songs to be included in the Eurovision competition from 1969 but had failed over and over again. In fact, those early failures were key to the formation of ABBA. They came 3rd for Sweden in 1973 and eventually made the finals in 1974 with Waterloo. They went on to become winners of the final leading to world-wide success. 

It was unusual for a pop group to have so many songs in the minor key which adds a sense of sadness and loneliness underneath the glamour of the disco sound they had. Perhaps the best example of this would be The Winner Takes it All which was reputedly written by Bjorn, about the breakdown in the relationship with Agnetha with the latter singing on the song.   

Their music has taken on a whole new dimension thanks to the musical Mamma Mia named after one of their biggest hits and featuring tracks from their back catalogue. It is still played in theatres where it is now the seventh-longest running show in West End history. In 2008, a film of the same name was made starring Meryl Streep, Pierce Brosnan and Colin Firth.