First, a bit of history. Björn Ulvaeus and Benny Andersson were introduced in June 1966 when they were both in other bands. Three years later, they met singers Agnetha Fältskog and Anni-Frid Lyngstad, and the quartet quickly turned into two romantic couples. Ulvaeus would later marry Fältskog, while Andersson went on to wed Lyngstad.

Despite all four being musicians, they didn't start producing music together until the early 1970s. Using the band name Björn & Benny, Agnetha & Anni-Frid, the group released the single People Need Love in 1972. This was followed by their album Ring Ring, which became one of Sweden's biggest hits in 1973.

After coming third in Melodifestivalen (the Swedish selection process for Eurovision) that same year, the group – which had rebranded to ABBA by that point – enjoyed more success in 1974 when they won not only Melodifestivalen but also the Eurovision Song Contest with Waterloo. Their victory was a fast track to global fame and, by 1979, the band was making net profits of $15 million a year thanks to record sales, merchandise, and other revenue streams. When adjusted for inflation, that's the equivalent of $68 million (£51m) today.

Money, money, money: which ABBA star is richest today?