Björn Ulvaeus was guitarist and singer for the Swedish pop group Abba, one of the most commercially successful bands of the '70s.

He was born April 25, 1945, in Gothenburg, Sweden. Ulvaeus was part of a folk-rock band called the Hootenanny Singers in the '60s. In 1966 he began writing songs with future Abba mate Benny Andersson. The two had a global smash in 1972 with "People Need Love," which featured Agnetha Fältskog (Ulvaeus' then-girlfriend) and Frida Lyngstad on backing vocals.

The four used the name Abba (an acronym of their first names) to enter the 1974 Eurovision song contest, which they won with "Waterloo." The song eventually became an international hit.

In 1975, "S.O.S." (RealAudio excerpt) became a smash for Abba in the U.S., UK and many non-English-speaking countries.

More global hits followed, including "Fernando," "Dancing Queen" (a U.S. #1 hit), "Knowing Me, Knowing You" and "The Name of the Game."

By the beginning of the '80s, the members' divorces (Ulvaeus and Fältskog had become husband and wife, as did Andersson and Lyngstad) began to tear apart the group, which officially broke up in 1982.

Ulvaeus and Andersson, who wrote many of Abba's hits, collaborated with Tim Rice on the musical "Chess" (from which Murray Head had a #3 U.S. hit in 1985 with "One Night in Bangkok"). Abba's music, as collected in two volumes of Abba Gold, continued to be popular worldwide in the '90s.

"Mamma Mia!" a musical written by Ulvaeus and Andersson and based on Abba's songs, began running in London last year. In 1998 the pair issued a Swedish-language LP.

Other birthdays Tuesday: Jerry Leiber, 67; Michael Brown (Left Banke), 51; Steven Ferrone (Average White Band), 50; and Ella Fitzgerald, 1917–1996.