In the episode, Adam asks Sheldon Cooper (Jim Parsons) to be in a documentary about his late father. As a lifelong fan of Star Trek -- and Leonard's character, Spock, in particular -- Sheldon is overwhelmed with excitement for the opportunity, but struggles to suppress his emotions about his recent breakup with Amy (Mayim Bialik) during the interview.
Leonard's work has had an indelible effect on The Big Bang Theory, despite never having been physically on the show. Sheldon dressed as Spock for a Renaissance faire in the second season, and in the fifth season, Sheldon had a dream in which a Spock action figure comes to life -- not to mention all the references to the iconic sci-fi series.
After Leonard's death earlier this year, Big Bang co-creator Chuck Lorre paid tribute in his signature vanity card for the 17th episode of season eight, titled "The Colonization Application." The producer posted a brief message underneath a black-and-white portrait of the Emmy-nominated actor.
"The impact you had on our show and on our lives is everlasting," the message read.
Leonard died at 83 on Feb. 27 at his home in Bel-Air due to end stage chronic obstructive pulmonary disease.