Star Trek: The Original Series
Star Trek "The Original Series" or TOS documents the initial voyages of Captain James T. Kirk aboard the first Federation starship to bear the name Enterprise. Even though the series was simply called "Star Trek" the subsequent addition became necessary for distinction purposes with the proliferation of new material in the franchise.
The show commented on many issues relevant to the era in which it was made: 1960s cold-war America. Certain civilizations were obvious analogies to real world superpowers; the United Federation of Planets was the USA, the Klingons were the U.S.S.R. and Romulans were Red China. Another common theme was for our intrepid explorers to encounter worlds that were the same as Earth but with one or two critical moments in history changed. One world even had identically shaped continents. It also tried to support activist movements of the time with the messages in its show, particularly the civil rights movement.
The series ran in three seasons, from 1966 to 1969. It was originally cancelled after its second season, but then renewed for a third after the networks couldn't find a suitable replacement show. A letter-writing campaign by the then-fledging fan base also helped but was far from the main reason why the series was renewed. However, with a slashed budget and the original writing staff all moving on to different jobs, the resulting "turd season" was generally viewed as not being worth the effort it took to produce, despite including a few half-decent episodes.