Only one Star Trek: The Original Series character was present for two of the apparent deaths of Captain James T. Kirk (William Shatner). Kirk definitively died at the end of Star Trek Generations, but there were two other notable moments when he was believed to have met his end. Firstly, in the TOS episode "The Tholian Web", Kirk was stranded aboard the USS Defiant when it passed into another universe. With only a few hours left in his oxygen tank, Kirk was assumed to be dead when the USS Enterprise failed to beam him to safety. Decades later, Kirk was aboard the USS Enterprise-B when he once again phased into another dimension.
Star Trek: The Original Series' Ensign Pavel Chekov (Walter Koenig) was present aboard both Enterprises during the Tholian and Nexus incidents. However, due to the mental instability caused by the dimensional interphase, Chekov was consigned to sickbay and was not cognizant of Kirk's apparent death. However, one member of the Enterprise crew who didn't succumb to the effects of the dimensional interphase was Chief Engineer Montgomery Scott (James Doohan) who also accompanied Kirk and Chekov on the first flight of the USS Enterprise-B.
