The world didn’t know how much it needed a Swedish Beatles until ABBA came along. With keyboardist Benny Andersson and guitarist Björn Ulvaeus as the songwriting geniuses and Anni-Frid Lyngstad and Agnetha Fältskog providing the vocal power, ABBA turned pure pop into high art, becoming one of the biggest groups on the planet. Before forming in Stockholm in 1972, Anni-Frid and Agnetha had been successful solo artists in Sweden, while Björn and Benny had been working as a duo; they became two married pairs as well as musical partners. The title track from their second album, 1974’s Waterloo, won the Eurovision song contest that year and became an international smash, introducing the world to ABBA’s seamless, epic production style (Phil Spector’s Wall of Sound taken to a celestial level), soaring melodies, and earworm hooks. ABBA owned the rest of the ’70s, scoring with blockbusters like the aching power ballad “Fernando,” the disco anthem “Dancing Queen,” and the sophisticated tapestry “Take a Chance on Me,” racking up multiplatinum sales, monopolizing pop radio worldwide, and becoming the mainstream pop stars it was cool for rockers (even Elvis Costello) to love. By the time of their final album, 1981’s The Visitors, both couples had broken up, and their formerly cheery tunes took a darker turn musically and lyrically. After 1982 they didn’t perform together again until a one-off at a party in 2016. Later, tantalizing announcements of new material in the works began. But as fans endured the wait, the theater and movie musical Mamma Mia! and the undying popularity of ABBA’s classics guaranteed them a continued place in pop culture.