"Enemy at the Gate" is the 100th and final episode of the science fiction television series Stargate Atlantis. The episode aired on January 9, 2009 on the Sci Fi Channel in the United States, and on January 13, 2009 on Sky1 in the United Kingdom. Written by Joseph Mallozzi and Paul Mullie as their fifth and final script in the fifth season, "Enemy at the Gate" was produced as the nineteenth episode of the season and was directed by Andy Mikita. It is dedicated to Don S.