Logan Nelson is a character from the Saw series, serving as the main protagonist and anti-hero of Jigsaw.
In flashbacks, Logan is revealed to have accidentally switched the names on John Kramer's X-ray, causing his cancer to be caught late. As a result, Logan along with Anna, Mitch, Ryan and Carly are placed in a bucket head trap where they must give any amount of blood by cutting themselves on a circular saw to survive the trap. Logan is unable to awaken from his sedation in time and is cut on the back but saved by John who recruits him as an accomplice, predating the events of Saw, feeling he should not be punished for an honest mistake.
Ten years after John's death, Logan arises suspicions that John may not be dead after exhuming his body and placing his blood underneath the fingernails of a trap victim. Logan recreated the very same barn trap gauntlet he participated in years ago using criminals who got off by the corrupt Detective Halloran, one of whom (Edgar Munsen) was responsible for the death of Logan's beloved wife, Christine. Logan slices Halloran's head into eight pieces using a laser collar trap, framing him as a copycat and with Eleanor's alibi, there is nothing to tie Logan with any of the deaths.