"Friend or Foe" is the first episode of the fifth season of the American animated television series SpongeBob SquarePants, and the 81st episode overall. It was written by Casey Alexander, Zeus Cervas, Mike Mitchell, Steven Banks, and Tim Hill, and the animation was directed by supervising director Alan Smart and Tom Yasumi; Alexander, Cervas and Mitchell also functioned as storyboard directors. The episode originally aired on Nickelodeon in the United States on April 13, 2007.

In the episode, Mr. Krabs reveals to SpongeBob that he and his business rival Plankton were actually best friends during their childhood. Through a series of flashbacks, Mr. Krabs tells the story of how that friendship deteriorated, the cause of their rivalry, why Mr. Krabs is obsessed with money, why Plankton became the villain he is today, and how the Krabby Patty sandwich was created in the process.

The episode received positive reviews upon release, and was released on DVD on April 17, 2007.