 Founded in 1971 in New York by Walter Becker and Donald Fagan. Originally having a full band lineup, but by the end of 1974, they chose to stop playing live and continue Steely Dan as a studio-only duo with a revolving cast of session musicians. So, yeah, that definitely counts as a duo as far as I'm concerned. Just like Holland Oates, they're the two guys whose names are on the band, but there's a full band set up behind them, so they've got a good one.