When John Constantine (Matt Ryan) appears on Legends of Tomorrow, fans can expect the character to develop a friendly relationship with the Legends' team leader, Sara Lance (Caity Lotz). Constantine previously crossed paths with Sara in his first Arrowverse appearance back in season 4 of Arrow.
Headlined by Ryan as the chain-smoking demon hunter, Constantine was cancelled by NBC after a 13-episode first season. Though the announcement of the show's cancellation upset fans who believed the series deserved another season, the character found new life when it was confirmed that Ryan's Constantine would return to TV as part of the Arrowverse. The character appeared in a season 4 episode of Arrow as someone from Oliver's past whose supernatural expertise was required to deal with a resurrected Sara Lance. It was later announced at New York Comic-Con 2017 that season 3 of Legends of Tomorrow would feature an appearance from Constantine.
On the set of Legends of Tomorrow, Caity Lotz talked to reporters about working with Matt Ryan and her character's relationship with Constantine. According to Lotz, Constantine's arrogance will be a problem early on, but the two will grow to be friends:
I’ve gotten to work with Matt before on Arrow, although I think I was possessed pretty much the whole time. He’s a fabulous actor; we had so much fun on set. I think Sara — he’s this really cocky guy who thinks he’s the s***, and I think Sara kind of throws him for a loop because he thinks he’s so impressive, but then she…takes everybody down. I think they’re friends — they like each other.
During season 4 of Arrow, Oliver asked for Constantine's help after Laurel used the Lazarus Pit to resurrect Sara. Unfortunately, Sara had been dead for too long for the process to work effectively. Sara went on an uncontrollable rampage until Constantine was able to perform a ritual that reunited Sara's soul with her body.
What we know about Constantine's guest appearance in Legends of Tomorrow is that the character will appear in the tenth episode, titled "Daddy Darhkest", which is also expected to revisit Darhk's death in the season 4 finale of Arrow.
Constantine fans can also catch the character in his own animated series which will premiere in 2018 on the CW Seed.
Season 3 of Legends of Tomorrow continues with "Helen Hunt" on November 14th on The CW.