'Legends of Tomorrow': Who Is John Constantine?

After a months-long hiatus, Legends of Tomorrow made its return tonight, and brought a DC Comics fan-favorite along with it.

Mild spoilers for tonight's episode of Legends of Tomorrow, "Daddy Darhkest", below!

Tonight's episode picked up right where "Beebo the God of War" left off, with Sara Lance/White Canary (Caity Lotz) being asked for help by John Constantine (Matt Ryan). As Constantine explained, he was tasked with performing an exorcism, only to find that the demon housed inside was Mallus (John Noble), the villain that has been lurking in the shadows of Legends' third season.

So, who is Constantine? And why are people more than a little excited about his return? Here's what you need to know.

John Constantine has been a fixture of the DC Comics and Vertigo world since 1984, when he made his unofficial debut in The Saga of Swamp Thing #25. The trenchcoat-wearing Brit functioned as a sorcerer, occult detective, and occasional con man who was secretly fueled by his guilt and post-traumatic stress. In particular, Constantine felt guilty about an exorcism involving a young girl, Astra, which ultimately sent her to hell.

Throughout the years, Constantine largely appeared in the Vertigo title Hellblazer, but a version of him was brought into the prime DC universe through the events of Brightest Day. The DC version of Constantine has sort of taken on a life of his own, especially as one of the founding members of Justice League Dark. Briefly, the Vertigo and DC Comics versions of Constantine appeared concurrently, until the Vertigo Hellblazer title concluded in 2013.

Since his debut, Constantine has become an increasingly-prominent character, with Hellblazer being Vertigo's most popular series. The character has since extended beyond the comic world quite a bit, appearing in film, television, and even rock songs.

He first entered the live-action space in 2005, when Keanu Reeves played the role in Francis Lawrence's Constantine. While the film arguably brought John Constantine to mainstream audiences, it was criticized here and there by fans, largely because of Constantine being very heavily Americanized and not looking much like his comic counterpart.

In 2014, Ryan took on the role, starring in NBC's Constantine TV series. The 13-episode first season followed Constantine on a journey around America, and crossing paths with various demons and supernatural threats. The show was cancelled in 2015, sparking a sort of movement amongst fans, many of whom were eager for Ryan to reprise his role in some capacity.

Later that year, fans got their wish, as Constantine was brought on to a special episode of Legends' sister show, Arrow. The episode saw Constantine's help being enlisted by Oliver Queen/Green Arrow (Stephen Amell) and Laurel Lance/Black Canary (Katie Cassidy), who were trying to rescue Sara's soul after her recent resurrection. At the end of the episode, Constantine parted ways with the group, spent a brief time literally in hell, and has now returned to team up with the Legends.

Outside of these live-action appearances, Ryan has also played Constantine in DC's animated space. The first instance was in the Justice League Dark animated film, which essentially exists outside of Constantine's live-action continuity. And he will soon reprise his role in an in-Arrowverse animated Constantine series, which is expected to debut sometime soon on CW Seed.

Legends of Tomorrow airs Mondays at 8/7c on The CW.