Kiss were far from their commercial peak when MTV agreed to film an Unplugged special in the summer of 1995. They had survived (and even thrived) during the disco and hair metal eras, but grunge proved too much to handle, and their 1992 LP Revenge failed to connect with fans or critics. They practically invented arena rock, but by 1995, they were playing to relatively small crowds at fan conventions.
Nostalgia for the 1970s soon became a very profitable business, and tours by Eagles, Pink Floyd and Jimmy Page & Robert Plant were packing arenas worldwide. The logical move for Kiss was to put the make-up back on and launch a 1970s nostalgia tour. That meant making amends with former members Peter Criss and Ace Frehley. Criss joined the band for a couple of old songs at a Kiss convention in the summer of 1995, and when they booked Unplugged a few months later, they invited the drummer along with Frehley to play alongside the current line-up.
The show ended with a completely unique version of "Rock and Roll All Nite," featuring all four original members singing verses of the 1975 classic. It must have been bittersweet for drummer Eric Singer and guitarist Bruce Kulick, since the move was clearly paving the way for a Kiss reunion tour that would exclude them. That tour did enormous business, but Singer rejoined the band in 2003 after Criss left for good. Ace Frehley parted with the group in 2002, but the band opted to replace him with Tommy Thayer instead of Kulick.
The original Kiss line-up hasn't played together in over a decade, but that might change in April when they are inducted into the Rock and Roll Hall of Fame. Gene Simmons has said he'll never play with Criss and Frehley again, but he's changed his mind on that in the past.