There are two bands and a singer with this name and also an ABBA tribute band:
1) Waterloo was a proto-prog outfit from Ghent, Belgium, active from 1969 to 1972. They recorded an album, "First Battle", in London in late 1969, produced by David MacKay and released on the French label Vogue in February 1970. Stylistically, the album is heavily influenced by "Stand Up"-era Jethro Tull and keyboard-based British prog bands of that era, such as Arzachel. Lead singer Dirk Bogaert later formed Pazop, while bassist Jean-Paul Musette became a member of Belgian RIO/zeuhl outfit Cos.
Line-up:
Dirk Bogaert - lead vocals, flute
Gus Roan - guitar
Marc Malyster - organ (replaced in 1970 by Frank Wuyts)
Jacky Mauer - drums
Jean-Paul Janssens - bass (replaced in 1970 by Jean-Paul Musette)
John Van Rymenant - saxophone (1970-1972)
2) Waterloo is John Baldus (drums, percussion), Chris Grabau (guitar, keyboards), Dave Melson (bass) and Mark Ray (guitar, piano, vocals). The songs are written by Mark Ray and arranged by the whole band, each member making distinctive contributions to the cumulative sound. Having released their first effort, Going To The Sun, to critical acclaim in 2001, Waterloo have spent the last two years playing the rare live show in Saint Louis and Chicago (with Pernice Brothers, Dolly Varden, among others) and devoting most of their time to writing, arranging, recording and experimenting for their second record, In The Light Of Day, released in march of 2004. In 2006 the band released their third album entitled Out Of The Woods.
3) Hans "Waterloo" Kreuzmayr was half of the Austrian duet Waterloo & Robinson. In the 1980s he had a solo career with songs like Im Land das Ewigkeit heißt.