Crisis on Infinite Earths has featured a number of new additions to the official Arrowverse canon - but none carries as much excitement and potential as Tom Ellis' Lucifer Morningstar. Both the character and the Welsh actor who plays him has undergone quite the journey over the years, on and off-screen. Loosely based on the character from Neil Gaiman's Sandman series, Lucifer began life as a procedural drama on Fox. After three increasingly praised seasons, the network officially canceled the show. Following a passionate fan campaign, however, Netflix stepped in to save it. Lucifer season 4 was released in mid-2019. Less than a month later, Netflix renewed Lucifer for a fifth and final season.
After it was announced that 2019's Arrowverse crossover event would be based on Crisis on Infinite Earths, speculation was rife. A variety of well-known figures from DC-related productions past and present were rumored. Such as Tom Welling reprising his Clark Kent role from Smallville and Kevin Conroy finally playing Batman in live-action were confirmed. Others, meanwhile, remained very much in the air. After it was leaked online that Ellis would make an appearance as Lucifer, the actor went on record to deny that he was involved in the crossover. Crisis on Infinite Earths Part 3, however, revealed Ellis' denial to be a lie. Visited by John Constantine, Mia Smoak, and John Diggle, Lucifer turned up as previously described.
Despite being spoiled for many ahead of time, the appearance proved no less exciting. Dominating much of the discussion on social media, Ellis' turn proved a highlight of the installment. And it is easy to see why. After playing Lucifer for almost half a decade, Ellis clearly has such a grip on the character to make it seem effortless. Exuding both charm and a quiet menace, Lucifer perfectly bounced off of Mia, Diggle, and Constantine respectively. It was Lucifer's interaction with the latter that proved most compelling, however - with many immediately calling for a Lucifer and Constantine spinoff. Whether or not such a project will ever come to fruition remains to be seen. That being said, stranger things have happened within the Arrowverse and the crossover established an existing history between the duo.
Fellow Welsh actor Matt Ryan debuted as John Constantine on NBC's short-lived and titular series: Constantine. After its own cancellation after one season, however, Ryan reprised the role in animation. Not long after that, he returned to live-action - first in a guest appearance on Arrow and then as a regular part of the team in recent Legends of Tomorrow seasons. As such, it's certainly possible that Ellis could make a similar jump if he desired - especially with Lucifer coming to an end. Equally, given the time-traveling nature of Legends of Tomorrow, it could easily be done without disrupting the beloved continuity of Ellis' titular series. Especially since his Arrowverse appearance was already established as being set before the events of Lucifer.
The introduction of Lucifer Morningstar also opens a lot of doors for the Arrowverse, thematically and in terms of storylines. After all, Lucifer's appearance confirms that heaven and angels exist within the shared universe. Not to mention Nephilim, the Angel of Death, and even Gaiman himself as God. All of that, plus no doubt many other kinds of unique beings, presents a wealth of potential for the Arrowverse to delve more positively into mystical and supernatural storylines. Equally, in the character of Lucifer, fans would get an antihero truly unlike any yet seen in the Arrowverse. Though each of the established shows have their fair share of diversity and representation, Lucifer would take things to a new level. Openly bisexual, sex-positive, and complex without excessive brooding, the possibilities provided by Ellis' and Lucifer's continued presence in the Arrowverse would be, to borrow a word, infinite.