The show, in addition to the tried and true, featured colorful new aliens, many that could never have been presented on TOS. Among the most memorable episodes was "Yesteryear," a time travel installment written by Dorothy C. Fontana. It brought back not only the Guardian of Forever, but also Mark Lenard as Spock's father, Sarek. And the story made fans think and even cry, especially the heartrending sequence in which a young Spock is set on his path to logic when he chooses to let his beloved pet, I Chaya, die with dignity.
Hal Sutherland directed most of the TAS episodes. He'd previously worked on such Saturday morning cartoons as The Adventures of Batman, The Batman/Superman Hour, Aquaman, Archie, Sabrina the Teenage Witch, Fat Albert and the Cosby Kids, The Superman/Aquaman Hour of Adventure and The New Adventures of Flash Gordon. Sutherland semi-retired not long after TAS ended its run, relocating with his family to Washington State, where he lived out the next several decades relaxing, pursuing his passion for painting and marveling at TAS's longevity. “The (animated) Star Trek series has continued showing through the years to new and older audiences throughout the world,” Sutherland told StarTrek.com during an extensive interview in March, 2011. “I recently received a letter from the Ukraine asking for a pair of autographs for a fellow and his brother who are still viewing the shows. It’s so amazing that the popularity is still there and seemingly everywhere. (Conventions) around the world are also fascinating (for me) to attend, with chances to meet childhood fans that are now grown and entertaining their own children with these shows that are still available on TV. Their thanks for the work we did back then is very personal and rewarding.”