 Following creator Gene Roddenberry 's suggestion that The Next Generation would be unable to afford an appearance by Leonard Nimoy as Spock , it was suggested in a memo that Mark Lenard could appear as Spock 's on @-@ screen father , Sarek . Lenard had made his first appearance as Sarek in the Star Trek : The Original Series episode " Journey to Babel " . Trent Christopher Ganino and Eric A. Stillwell began to work on a script involving both Lenard as Sarek and Denise Crosby as Tasha Yar . This was because Crosby told Stillwell that she wanted to return to the show after her character was killed off in " Skin of Evil " in the first season of The Next Generation . This script would change over time to become " Yesterday 's Enterprise " . 
