The vanity card at the end of Thursday's episode featured a picture of Nimoy with a caption that read, "The impact you had on our show and on our lives is everlasting."
Sheldon's obsession with Nimoy has been a running gag on "The Big Bang Theory." He's dressed up as Spock, played the game "Rock, Paper, Scissors, Lizard, Spock" and in another episode Penny gives him a napkin Nimoy used and autographed at a restaurant.
Nimoy never physically appeared on the show, but he did appear in a dream sequence (as the voice of a Mr. Spock action figure) during a 2012 episode.
After news spread of Nimoy's death on Feb. 27, members of the "Big Bang Theory" cast were among those who took to social media to pay their respects.