"Who Killed Archie?" is a storyline from the BBC soap opera EastEnders. It began on 25 December 2009, Christmas Day, when the character Archie Mitchell, played by Larry Lamb, was murdered by an unseen person. Events leading up to and following the murder put several characters in the frame, in the style of a Whodunit mystery. The culprit was kept a tight secret within the production crew as well, with only seven people knowing the identity of the killer. The murderer was revealed as Stacey Slater during a live episode titled "EastEnders Live", broadcast on 19 February 2010, the show's 25th anniversary. Turner was told thirty minutes before the broadcast that Stacey was the killer, and actors rehearsed several possible endings. Finally, a two-hander episode between Stacey and her ex-lover Max Branning on 26 March 2010 explained how she killed Archie - who had previously been the show's main antagonist prior to the character's death and murder storyline.

EastEnders is a British television soap opera created by Julia Smith and Tony Holland which has been broadcast on BBC One since February 1985. Set in the fictional borough of Walford in the East End of London, the programme follows the stories of local residents and their families as they go about their daily lives. Within eight months of the show's original launch, it had reached the number one spot in BARB's television ratings, and has consistently remained among the top-rated series in Britain. Four EastEnders episodes are listed in the all-time top 10 most-watched programmes in the UK, including the number one spot, when over 30 million watched the 1986 Christmas Day episode. EastEnders has been important in the history of British television drama, tackling many subjects that are considered to be controversial or taboo in British culture, and portraying a social life previously unseen on UK mainstream television.