Caution: potential spoilers.
This was a primetime soap, which ran from 1978-1991. Since I was only 2 or 3 when it started, I didn't see any of it until the mid-80s. Which means it had a lot of history I never knew about, and a lot of characters I never saw. (In fact, the most famous storyline, "Who Shot J.R.?" was from 1980, but I didn't hear of it until much later. It was actually parodied in a 1995 two-part Simpsons story, "Whow Shot Mr. Burns?" though I had heard of the J.R. thing well before that.) The other most famous event from Dallas's history came in 1986, in the season finale, when Bobby Ewing turned out to be alive (after having been dead all season, because his actor, Patrick Duffy, had left the show). I actually remember seeing that episode. In the next season's premiere, it turned out that the entire previous season had been a dream his wife Pam had had (it's possible the dream season was the first season I ever watched, I'm not sure). Um... I should also say that at some point, I got reference book, which was published in 1985 (though I think I probably got it a few years later; I think it's something Dad got me at a yard sale or something). So I learned about some history and characters from that, though now I remember pretty much none of it.
Anyway... the show was about the Ewings, who were this rich family in Dallax, Texas, who owned an oil company (and who lived at Southfork Ranch). But of course there were plenty of other families in the show, most of them rich, as well, and in oil. The main character was J.R. Ewing (played by Larry Hagman, previously of I Dream of Jeannie), who was married to Sue Ellen (who we liked; played by Linda Gray). They had a son named Jon Ross III. Sometime before I started watching, J.R.'s father, Jock, had died, but J.R's mother, Miss Ellie, was still around. And um, J.R. had a brother named Bobby, who was married to Pamela Barnes (who we liked; played by Victoria Principal). Her brother, Cliff Barnes, was J.R.'s main business rival (he was the son of "Digger Barnes," a rival of Jock's, though Digger died before I started watching the show). Well, there were tons of other characters, and being a soap, there were plenty of changes in marital status. At some point, Bobby married a woman named April Stevens (who we liked; played by Sheree J. Wilson, who I'd later see in Walker, Texas Ranger). Um... I guess Jock and Miss Ellie had three sons. J.R. was the oldest and Bobby was the youngest; the middle child was Gary, who I don't recall ever seeing on the show. Apparently, he was mostly in the spin-off series "Knots Landing," which I never really got into. Gary had a daughter named Lucy (who I don't remember well, but I'm sure we liked). Also, Jock had an illegitimate son named Ray Krebbs, who was the foreman of Southfork Ranch. And Miss Ellie had a second husband, after Jock died, named Clayton Farlow. J.R. had a secretary named "Sly," who according to Wikipedia was his fourth secretary, but she's the only one I ever saw. J.R. and Sue Ellen had a son named John Ross III. Bobby and Pam had an adopted son named Christopher. In the last couple seasons, an illegitimate son of J.R.'s was introduced, named James Beaumont. And in the last couple seasons, J.R.'s main rival was Carter McKay. And J.R. had a second wife named Cally (who I don't remember well, but I'm sure we liked). I'm sure in addition to the many characters I never saw, there were many I did see, but am completely forgetting.
Anyway, J.R. was an egotistical, manipulative, cheating, totally unethical son of a... *ahem* He was a very interesting character. Bobby was a much nicer guy. I don't remember much in the way of actual plots, though there was one time J.R. checked himself into a mental hospital to get a patient's signature, but ended up being kept there against his will for awhile. That was fun. And the series finale, in which some like "guardian angel" or whatever was showing J.R. what people's lives would be like without him (a la It's a Wonderful Life). And it ended with something that made it seem J.R. had shot himself. Five years later, in 1996, there was a TV movie, J.R. Returns (which I should watch again someday and write a review of). The only thing I remember about it is that it confirmed something I had predicted since I first saw the series finale. In 1998, there was another TV movie, War of the Ewings, which I've never seen. And in 2012, TNT started a new series which continues the story of the Ewings, which is also called Dallas.