question: What American actor who appeared on the twelfth episode of The Simpsons fourth season was "The Princess Guide" dedicated to?
answer: Leonard Nimoy
context: Title: Everything is Broken (Defiance)
  Passage: "Everything is Broken" is the twelfth episode of the first season of the American science fiction series Defiance, and the series' twelfth episode overall.  It was aired on July 8, 2013.  The episode was written by Kevin Murphy and directed by Michael Nankin.
  Title: Revelations (Battlestar Galactica)
  Passage: "Revelations" is the twelfth episode in the fourth season of the reimagined "Battlestar Galactica".  It first aired on television in the United States on June 13, 2008.  The episode serves as the mid-season finale of the fourth season, with the concluding episodes of the series airing after a hiatus.  The survivor count shown in the title sequence is 39,665.
  Title: Leonard Betts
  Passage: "Leonard Betts" is the twelfth episode of the fourth season of the American science fiction television series "The X-Files".  It premiered on the Fox network on January 26, 1997.  It was written by Vince Gilligan, John Shiban, and Frank Spotnitz, directed by Kim Manners, and featured a guest appearance by Paul McCrane as Leonard Betts/Albert Tanner.  The episode is a "Monster-of-the-Week" story, unconnected to the series' wider mythology.  "Leonard Betts" was Fox's lead-out program following Super Bowl XXXI and was the most watched episode of the series, receiving a Nielsen household rating of 17.2, being watched by 29.1 million people in its initial broadcast.  The episode received positive reviews, with critics commenting positively on the character of Betts and McCrane's performance.
  Title: The Princess Guide
  Passage: "The Princess Guide" is the fifteenth episode of the twenty-sixth season of the American animated sitcom "The Simpsons", and the 567th overall episode of the series.  It originally aired on the Fox network in the United States on March 1, 2015.  The episode was dedicated to the memory of Leonard Nimoy, who died two days before the episode aired.  Nimoy guest-starred in two "Simpsons" episodes, "Marge vs. the Monorail" and "The Springfield Files".
  Title: Marge vs. the Monorail
  Passage: "Marge vs. the Monorail" is the twelfth episode of "The Simpsons"' fourth season.  It originally aired on the Fox network in the United States on January 14, 1993.  The plot revolves around Springfield's impulse purchase of a faulty monorail from a conman.  The episode was written by Conan O'Brien and directed by Rich Moore.  Recurring guest star Phil Hartman provided the voice of Lyle Lanley, while the American actor Leonard Nimoy made a guest appearance in this episode.
citations: The Princess Guide Marge vs. the Monorail