Meet John P. Wise. John was the former backup to the Cincinnati Bengals' Who-Dey mascot. Most of his work included getting chucked in the jewels and bringing tons of Who-Dey goodness to party goers. The Who Dey is a funny thing. Saints fans are convinced that the Bengals ripped them off. This Bengals Jungle piece explains that the Who Dat (the Saints version) came into existence after Steve Monistere marketed the chant in 1983. Then took a break until 1987. The only time the chant was used in early Saints history was when they played well -- which wasn't often. In fact, it's claimed in that article, that the Who Dat chant was ripped off from LSU.
You can trace Who Dey back to 1981.