 William Shatner reprises the role of Admiral James T. Kirk , Starfleet officer . Shatner remarked that being directed by Leonard Nimoy , his longtime co @-@ star and friend , was initially awkward , although as the shoot went on , it became easier as Shatner realized how confident Nimoy was . To reduce weight , Shatner <unk> before the start of production , but as filming continued , he tended to " slip " ; the costume department had to make 12 shirts for him . In his book with Chris <unk> , Star Trek Movie Memories : The Inside Story of the Classic Movies , he believes that the scene where he learns of his son 's death is " Kirk 's finest celluloid moment ever " . 
