Lucas Johnson is a fictional character from the BBC soap opera EastEnders, played by Don Gilet. He made his first on-screen appearance on 3 April 2008. Lucas is introduced as a reformed drug addict and criminal-turned-preacher who appears as the estranged father of established character Chelsea Fox (Tiana Benjamin/Zaraah Abrahams). He also has a young son, Jordan Johnson (Michael-Joel Stuart), and later goes on to marry Chelsea's mother, established character Denise Fox (Diane Parish) - whom he had previously been in a relationship with prior to their reunion.

While the character originally appeared to be respectfully dedicated to his own religious convictions, Lucas slowly became the show's secondary antagonist when he causes the death of his former wife Trina (Sharon Duncan Brewster) by leaving her to die in a raking accident; murders Denise's ex-husband Owen Turner (Lee Ross) on their wedding day; drowning his son's dog Sugar after the latter risks unearthing Owen's corpse; and strangling Denise before locking her up in a basement while allowing her family to believe that she is responsible for the murders - with Lucas killing another woman to use as Denise's supposed body so that her family could believe that she committed suicide. The character soon departed on 30 July 2010 when Lucas gets arrested for the murders of Trina and Owen, both of which were publicly exposed after he allowed Denise to escape and she subsequently exposed his homicidal crimes to her family - which resulted in Lucas briefly holding Denise and her family hostage until he eventually turned himself in. Lucas made a previously unannounced reappearance on 1 January 2016 before returning for a short stint in the year, in which he escaped prison until he was rearrested and left the programme again on 10 March 2016. On 1 October 2020, it was announced that Gilet was set to reprise his role, and he returned on 25 December 2020 and departed on 18 March 2021. He made an unannounced return on 31 January 2024.

During his time working on the show, Gilet has described Lucas as having "Jekyll and Hyde" aspects to his character. This multi-faceted personality was further explored in the BBC Three special EastEnders: The Two Faces of Lucas. The character also appeared in the spin-off series EastEnders: E20.

Gilet's casting in the show was announced in January 2008, when the character was described as "attractive, charismatic, strong and forthright" and "just a dodgy geezer with a murky past." His profile on the official EastEnders website describes him as "an upstanding member of the community, a far cry from the youth he once was." Through the show's narrative, it is revealed that Lucas is a former drug addict and has gone on to become a preacher in a Christian church.

In February 2009, it was announced that Sharon Duncan Brewster had been cast as Lucas's estranged wife Trina. Entertainment website Digital Spy reported: "Trina arrives and surprises Lucas and she makes it very clear she wants to give things another go. Lucas tries to get rid of her but his secret is out when Patrick (Rudolph Walker) sees what's going on. Just how willing will Trina be to let her husband walk into the arms of another woman? And more importantly, will she divorce him to enable him to marry again?" Despite his connection with the church, in September 2009 Lucas attempts to cover up his involvement in Trina's death. Gilet told Soaplife magazine, "When he first appeared someone wrote in saying he was a good character, but somewhere down the line something was going to come unstuck. We've always known there was more to this do-gooder than meets the eye. Things are going to get a lot darker in the build-up to Christmas. [...] It's going to get very dark and I hope I can pull it off." Lucas went on to kill Denise's ex-husband Owen Turner (Lee Ross) when he came close to discovering how Lucas was involved in Trina's death. Gilet explained that although Lucas does not want people dead and has no malice in his heart, he sees killing as a way to stop things from happening. When the show's executive producer Diederick Santer was asked by Digital Spy what was lined up for Lucas in 2010, he said "He's got right on his side, hasn't he? Is the world a better place without Trina? Probably, yes. Is the world a better place without Owen? Well, I don't know about that, but he's not a particularly nice person... Lucas is doing the Lord's work and who knows what that's doing to his head maybe he'll kill again. Lucas's story is 'poised' and we're just trying to work out the exact timing of the long-term story. There's brilliant stuff in the pipeline — it's one for a slow burn really. We have Lucas who's a murderer. Will he murder again? Who's the next person to cross him? He's one dangerous man."

Gilet described Lucas as having "Jekyll and Hyde" aspects to his character, and tries to hide the darker side of his personality from Denise. Gilet commented: "Every actor enjoys playing a character who's flawed – but how long can Lucas continue to hide the dark side of himself before the cracks start to show? I think a lot of people reckon the clock might be ticking. This story has shocked some people! I was getting fan mail where people were saying what a nice guy he was – and, of course, now they know he's not." Gilet has called Lucas "a very good character to play because of his complexity", explaining: "I think that's partly because he's a guy who always strives to do the right thing but his path for doing that gets warped as time goes on. I think his heart started off in the right place but - partly because of his drug-addled years - he has a slightly warped outlook on life." Asked whether he felt Lucas was truly bad, Gilet replied:

On the surface it doesn't seem that bad and he thinks he's got a good moral sense of right and wrong but if you push through and try to find what's at the kernel of who he is, you'll probably find a very angry character. He's got a lot of rage in him and he's using God as a kind of anger management that kicks him on the right track. When he has problems and his world is threatened - something he's worked so hard for over the years and he's an upstanding member of the community, people look to him and respect him - when that's threatened, when people like Trina come back into his life, it's his past returning. That's when the complexity comes in.

— Don Gilet, Digital Spy