Eureka first used the name "The Boss" on a basic Dial-a-Nap bag-first upright way back in the early 1990's. I guess it was meant to define a "back to basics," "no nonsense" powerful no frills vac. Costing no more than $100 with a set of attachments, Consumer Reports rated this a Best Buy in their upright category, and I think it ranked Number Two in the long list of uprights tested. In those days, performance when using the attachments was not a factor in ranking uprights.
With the success of this basic Boss upright, Eureka began to plaster the name The Boss on one version of every line of vacs they sold. They usually chose the bottom of the line-up as the Boss version - no nonsense, basic, no frills version in each line-up they had: the Bravo, the Victory, the Rally, the World Vac, the Excalibur, even the rechargeable Quick-Up "Boss Lite"....
At some point, even the parent company Electrolux of Sweden began to sell Boss vacs in Europe.
It kind of reminds me of how Hoover began to use the name Turbopower on specific versions of vac in each of their line-ups. Not sure if these were the low end models of the line-ups or not...