This image released by HBO shows Regina King in a scene from "Watchmen." (AP Photo)

For years, “Watchmen” stood alone as one of, if not the greatest comic series in history.

Now it’s getting sequels on the page and screen.

HBO’s “Watchmen” series premiered Sunday, about two months before DC’s 12-part “Doomsday Clock” series wraps up — more than two years after the first issue hit stands.

The original series, written by Alan Moore with art by Dave Gibbons, debuted in 1986 and portrayed a world populated by superheroes with only one actual superhuman: the nigh-omnipotent Doctor Manhattan. Most of them had been forced into retirement with the passage of the Keene Act, which banned all costumed crimefighters but those supported by the U.S. government.

The most infamous of the remaining “heroes” was the Comedian, a brutal agent whose murder sets the comic’s plot in motion. Investigating the mystery is the violent vigilante Rorschach, who defies the law and keeps fighting what he considers the good fight. His face hidden behind his distinctive mask, Rorschach tries to enlist the aid of former heroes Dan Dreiberg (Nite Owl), Adrian Veidt (Ozymandias) and Laurie Juspeczyk (Silk Spectre), who is romantically involved with Doctor Manhattan.

The search for answers about the Comedian’s death plays out amid flashbacks to the characters’ past and a look at how superheroes would affect the “real world.” The results are not as glitzy, optimistic or exciting as the comic book stories of yesteryear, with the story examining the damaged psyches of people who try to improve the world through violence and the ramifications of their actions on a personal and political level.

The series is absolutley not for kids. It’s violent and unsettling, but not in an exploitative way; it’s a function of the story. Doctor Manhattan’s disdain for wearing clothing may surprise some, but the nudity isn’t there for shock value. Sometimes it just doesn’t make sense to have a strategically placed tree branch in the scene.

The series was originally pitched with characters DC had acquired from Charlton comics, but the decision was made to merge those heroes into the existing DC universe. So Moore retooled them, with Rorschach replacing the Question, Doctor Manhattan standing in for Captain Atom, Nite Owl instead of Blue Beetle, Comedian in place of Peacemaker, Silk Spectre for Nightshade and Ozymandias instead of Thunderbolt. Grant Morrison revisited the concept with these characters in the 2014 “Multiversity” story.

Other than some winking references, the “Watchmen” characters remained untouched for a couple of decades. In 2012, DC launched “Before Watchmen,” a series of prequels with top-level talent crafting new stories set, well, before “Watchmen.” Despite the impressive lineup, the series were not very well received (particularly by Moore, who maintains the original story should stand alone).

The lasting legacy of “Watchmen,” coupled with the watershed “Dark Knight Returns” around the same time, was an emphasis on “grim and gritty” comics and efforts to make them more “realistic.” Their success varies from story to story, but too often it seems, people focus on the darkness of “Watchmen” without the quality and story to support it.

In 2016, DC dropped a bombshell by revealing the landmark “New 52” sort-of reboot five years earlier was somehow tied to “Watchmen.” Skeptical though I was, the concept was exciting.

That led, eventually, to “Doomsday Clock,” taking place about a year after the events of the ’80s-set”Watchmen” and slightly ahead of the present DC universe. It promised a battle between the ever-optimistic Superman and Doctor Manhattan, whose insights into the building blocks of existence drove him further and further from his humanity, to a cold practicality.

Aside from the constantly delayed release schedule, the series got hung up early on with a pair of mysterious new characters. The tale jumps around a lot, interspersing important revelations with drawn-out subplots. I want to get the final issue and reread the series before I fully assess it.

HBO’s “Watchmen” is set many years after the comic and is apparently aims to follow the spirit and ideas of the comic rather than adapt it.