Whose Line was an incredibly popular improvised sketch comedy show -- adapted from the original British version -- wherein a cast of performers would be given scenes and characters to act out on the spot. The show aired for over five years in the States and was recently revived in 2013. Because of the shows enormous popularity in the late 1990s and early 2000s, a handful of special guests appeared from time to time. These guests ranged from Whoopi Goldberg to fitness guru Richard Simmons. In 2000, during the shows third season, Whose Line landed arguably its biggest guest ever in Robin Williams. Robin was perfectly suited to the idea of the show, as much of his comedy was outlandish and off-the-cuff. Quite simply, Robin stole the show -- as he was doubtless expected to do. He performed various impressions -- notably one of Carol Channing. Furthermore, laughs were elicited when Robin would have trouble containing himself to the shows confines, venturing outside of the norms. The appearance on Whose Line Is It Anyway was by no means a great feat of acting or an important piece of Robin Williams acting career. What it was, however, was an opportunity for Robin to cut loose -- as only he could -- and entertain an audience.