- "Your articles are honest and smart. I could never write the way you write."
"You have two Pulitzers."
- "It's not from the writing. It's from the story. I have craft, you have art."
- —William Dey and Kara Danvers[src]
William "Will" Dey is a renowned reporter, formerly of The Times, Le Monde (The World), and the Daily Mail. He is currently a resident of National City, and a reporter of CatCo Worldwide Media. He was at odds with his co-worker Kara Danvers as he was undercover to learn more about Andrea Rojas and her role in the death of his best friend Russell Rogers.
At various points in time, William started working as a reporter for The Times, Le Monde, and The Mail; he eventually resigned from them all. At some point, he was renowned for his article on eminent domain in Hartlepool.
In October 2019, William started working at CatCo Worldwide Media. Andrea later introduced William to Pulitzer Prize-winning reporter Kara Danvers, who didn't make a good first impression for him due to her mispronunciation of the town name Hartlepool. Andrea consulted Kara on William rewriting her article on the governor's proposed water tax, an action Kara took offensively as it had all the necessary facts. William explained that the piece was filled with too much unnecessary information and reasoned that every piece has inherent bias, which was the complete opposite of what Kara expected him to say, due to his reputation from when he was still working with The Times of London; William clarified his works were of their respective natures solely due to the orders of his former superiors. In her suppressed outrage, Kara cleared up what she will and will not tolerate concerning her works, to both Andrea and William's surprise and reaffirmation of her resolution.
At a nightclub, William approached a man and once again demanded that he reconsider working together. The man again declined, before leaving. The next day at work, Andrea Rojas wanted a "sparkly" story of murder. When coming across billionaire, Niles Jarrod who died at a club, she waved it off as nothing important, and William supported her in this. Kara and William found themselves in a verbal altercation. William told the room he had already looked into it, and there is nothing there. Afterwards, Kara confronted William outside about why he was lying. He blew her off, calling her paranoid. Later, William was sitting on a park bench. A man passed him a rolled-up newspaper with money inside of it.
William is working undercover for the London Times and trying to expose Andrea's corrupt schemes.
He was the best friend of Russell Rogers, also known as Rip Roar. Russel was dating Andrea Rojas, and expressed his concerns about her family when they once met at a bar. After becoming Rip Roar and while leaving his house, Russel was confronted by William. William became convinced the Andrea Rojas and Rip Roar were involved in Russell's death, and begun to pursue this to the point of obsession. 
During the Anti-Monitor Crisis, William as well as everyone in the multiverse except for the seven Paragons, was killed in an antimatter wave by the Anti-Monitor on December 10, 2019, only to be restored a month later, after the Paragons and the Spectre created a new universe.
William's life appears to remain the same, after the creation of Earth-Prime. He still works as a reporter for CatCo, determined to expose the truth. He is motivated by the fact that his best friend, Russell Rogers, died under suspicious circumstances after turning down a deal from Lex Luthor, leading William to believe Lex is not the good guy he claims. However, in this timeline he joined CatCo to get close to Lena Luthor instead of Andrea Rojas.
William and Kara accompany each other to a toy convention where they run into Lex, much to his own seething anger. After some hostile questioning about a possible murder, Lex removes himself for a word with Kara. Back in the office his conversation with Kara about his pending theories on Lex are interrupted when their boss Andrea calls for them. The next day he reveals photos of Lex at Fort Harrison paying off security guards, they decide to work together. After, Kara invites him to her apartment along with the rest of her friends for drinking and games.  Kara later invites him to karaoke night, and after admitting his favorite song to karaoke to is ‘Africa’, Kara’s sister convinced them to sing a duet together. She is soon called away by her sister for help with their sick grandmother. Days later she finds him during the temporary blackout at the office. After presenting Kara with a puzzle for her grandma, and asking her out, Kara politely turns William's romantic advances down. He thanked her for her honesty, and promises there are no hard feelings. 
Learning about Eve
Before work, William brings Kara and Nia coffee. He is assigned to cover his boss' campaign trail for Obsidian Platinum despite her being attacked in the elevator earlier. He agrees, and runs into Supergirl who is Andrea's bodyguard for the day. While talking about his co-worker Kara that he admires, they are interrupted when Andrea is attacked for a second time. 
The next day, William meets with Kelly Olsen and discuss Alex and Kara's loss of their father. He confirms Kara has already returned home for the funeral, and Kelly admits Alex Danvers is angry and refuses to go. Later William begins looking into trial users for Obsidian North lenses. The mass majority of whom are simply binge watching their existence. However approximately 50 names are all unresponsive and located at the same address. Though William goes to their location, Margot Morrison makes them invisible to him; he only leaves with a hospital bracelet.
The next day, he and Kelly research the manifesto video that was left behind when Lex was forced to kill Margot to save her kidnapping victims. They learn that it was Eve Teschmacher using an image inducer. When he takes his findings to Andrea, she harshly dismisses him and tells him that he needs to stop trying to delay the launch of her work. William decides to work solo to keep Kelly from further trouble.
William was following Eve when she stepped into an alley; as he looked through the alley, a black sack was placed over his head. At gunpoint, William was confronted by Eve, who explained that she worked for Lex because her mother is being threatened; William promised that if he was released he would help her to expose Lex and free Eve Teschmacher's mother. Eve did not believe him and shot him anyway; just then, Supergirl and Lena Luthor arrived. Supergirl cauterized the gunshot wound that had totally gone through William's shoulder. He worried about the welfare of Kara Danvers, but Lena assured him that she knew that Kara was safe.
William at first appeared to act highly of himself and look down on others but in reality, this was an act. He started as an arrogant jerk. He sounded like Andrea's lapdog, with his criticizing of Kara's work. It was eventually revealed he is actually a nice guy and he cares about people. The arrogant jerk is just an act. He is working undercover for the London Times and believes that Andrea and her family are criminals. It is the main reason why he workes at CatCo and treated Kara badly because he wants to take down Andrea and her family, and avenge the "death" of his best friend. So, he became Kara's new ally.
- Expert investigator: William has earned a big reputation working with The Times, Le Monde, and The Mail. Being well renowned for his stories. Even being able to track down Kara Danvers while she was Supergirl. He has excellent perception and empathy towards a person's nature. Despite being held at gunpoint by Eve Teschmacher, he correctly deduced that she was not truly a villain, but rather being forced to commit such actions under threat of her mother's life.
Behind the scenes
- William is the third main character on who doesn't have a comics counterpart, after Alex Danvers and Kelly Olsen.
- However, Nia Nal is an original character while her alter-ego of Dreamer isn't. Nia is based off Nura Nal who in the show is her descendant.
- Staz Nair previously played Dax-Baron, the Kryptonian alter-ego of super-villain Doomsday, in Krypton.
- This is the second actor portraying Doomsday to star on Supergirl after Sam Witwer played Davis Bloome, the human alter-ego of Doomsday on the show Smallville.