 Nimoy had admired Christopher Lloyd 's work in One Flew Over the Cuckoo 's Nest and Taxi , and was impressed by his ability to play powerful villains . Lloyd was given the part of Kruge , a Klingon interested in securing the powerful secrets of Genesis for use as a weapon . Nimoy said that Lloyd brought a welcome element of theatricality to the role . Mark Lenard plays Sarek , Spock 's father and a Vulcan ambassador . Lenard had previously played the role in the television episode " Journey to Babel " . Merritt Butrick appears as David Marcus , Kirk 's son , a scientist who had helped develop the Genesis Device . 
