Dallas came first. The show debuted on April 2, 1978, as a five-part miniseries on the CBS network while Dynasty first in aired on January 12, 1981.
Dallas, created by David Jacobs, went on to become the most successful show in the history of television.
The original storyline was Romeo and Juliet retold — two young people from opposing Texas oil families fall in love.
Dallas didn’t become a hit until a villain emerged. Larry Hagman’s portrayal of J.R. Ewing as an immoral, vindictive businessman gave viewers a vicarious thrill. The character was so powerful, that on the evening of November 21 , 1980, the nation ceased normal activities to find out “Who Shot J.R.?”
The shooting took place in the final scene of the third season, creating the very first cliffhanger of primetime TV. Trying to guess the “whodunit” became a worldwide obsession.
The episode that revealed the answer sent ratings higher then anything TV had ever seen, with numbers that even beat the Super Bowl.
In 1981, ABC took note of the soap opera “Dallas” and drafted its own drama about a wealthy family in the oil business, “Dynasty,” and laid the luxury and glamour on thick.
However, ratings dropped during the first season, so just like on “Dallas,” the producers decided to shake things up and add a villain.
British star Joan Collins entered the show in season two as Alexis Carrington, Blake Carrington’s ex-wife and a female version of J.R. Ewing. “If you look at the actors in ‘Dynasty’ they were probably the best looking actors I have ever seen in a show — better then ‘Dallas,’” said Joan Collins. - See more at PBS.org.
See a list of the 10 best soap operas of all time, featured on ThoughtCo.com.