"Stone Cold" Steve Austin against Vince McMahon and almost the entire locker room of wrestlers during their feud in the WWF attitude era, notable in the 1999 Royal Rumble. Classic one man army against corporate power. Stone Cold ultimately emerged as the victor of their 2 year long feud. Oh Hell Yeah!
In many cases in 1997, Sting was a One Man Army when taking on the nWo—over the course of that year, he ended up taking out the entire group on multiple occasions, all in a bid to get his hands around Hogan's neck.
WCW had another in Goldberg, who squashed so many people that the announcers started keeping track of his win-loss record.
Jaider Lee in the Bolivian New Xtreme Order, whose sheer speed, stamina, agility and savvy in regards to wrestling moves allow him to fight multiple opponents by himself for extended periods of time.