"Who Dat" became famous as part of a chant for fans cheering on the New Orleans Saints ("Who dat say dey gonna beat dem Saints!). As a result, Saints fans have been dubbed "Who Dats."
It has been debated exactly where it started, but some claim it began with Southern University fans either in the late 1960s or early 1970s and went "Who dat say dey gonna beat dem Jags" - Southern University being nicknamed the Jaguars.
Another claim is that around the same time it began at St. Augustine High School, a historically African-American all boys Catholic high school in New Orleans, and then spread to the New Orleans Public Schools.
Another claim is that the cheer originated at Patterson High School in Patterson, Louisiana (home of Saints running back Dalton Hilliard).
By 1983, the New Orleans Saints organization officially adopted it during the tenure of coach Bum Phillips, and Aaron Neville (along with local musicians Sal and Steve Monistere and Carlo Nuccio) recorded a version of "When the Saints Go Marching In" that incorporated the chant (performed by a group of Saints players) that became a major local hit, due in part to the support of sportscaster Ron Swoboda and the fact that Saints fans had been using the chant already.