Star Trek: The Animated Series (often referred to simply by the abbreviation "TAS") was an important part of the Star Trek cannon for a few reasons: it bridged the gap for content-hungry fans between the end of the original series in 1969 and the debut of first film (Star Trek: The Motion Picture) in 1979, it was the first to win an Emmy award, and the first on-screen instance in which fans heard that the "T" in James T. Kirk stood for "Tiberius."
The series ran from 1973-74 and continued/supplemented many of the storylines from the original series. It also featured the voice talents of William Shatner, Leonard Nimoy, DeForest Kelley, George Takei, James Doohan, Nichelle Nichols and Majel Barrett (the only member of the original cast missing was Walter Koenig as Pavel Chekov). While it was popular among many adult fans and critics, the show failed to garner enough of the children's market as originally intended, and it was cancelled after a total of only twenty-two episodes.
Currently available from CBS/Paramount is a four-disc DVD set that includes all episodes from the series as well as multiple bonus features, including Show History (a simple slideshow-esque collection of facts about the show), a storyboard gallery, audio commentaries (with fun behind-the-scenes info) and text commentaries (pop-up trivia), What's the Star Trek Connection? (a grouping of mini features that draw lines between the show and other Trek movies and television series), and Drawn to the Final Frontier—The Making of Star Trek The Animated Series (a documentary on the life of the animated series from its beginnings to its reception today, featuring interviews with the creators including D.C. Fontana (producer), David Gerrold (writer), Hal Southerland (director), and Lou Scheimer (series producer).
Mega-fans who want to own anything and everything Star Trek will, of course, want this set (snaggable on Amazon for $12.81) in their library. However, before you buy it for yourself or for someone as a gift, be aware that this set has the same episodes and bonus features as the 2006 set released a decade ago, so there is a chance you/they actually already have it. The episodes themselves are also currently available on Amazon Prime and Netflix, so even if you're a diehard Trekkie, consider all the available options before purchase.