Last month, between tweets disputing his election loss, President Trump posted an article from a conservative website that said his sister, Elizabeth Trump Grau, had just joined Twitter to publicly back her brother’s fight to overturn the vote.

“Thank you Elizabeth,” Mr. Trump wrote on Twitter. “LOVE!”

But the Twitter account that prompted the article was not his sister. It was a fake profile run by Josh Hall, a 21-year-old food-delivery driver in Mechanicsburg, Pa.

“I was like, ‘Oh, my goodness. He actually thinks it’s his sister,’” Mr. Hall, a fervent Trump supporter, said in an interview last week.

It was a surreal coda to nearly a year of deception for Mr. Hall. Since February, he had posed as political figures and their families on Twitter, including five of the president’s relatives. He had pretended to be Robert Trump, the president’s brother; Barron Trump, the president’s 14-year-old son; and Dr. Deborah L. Birx, the White House coronavirus response coordinator. The accounts collectively amassed more than 160,000 followers.

Using their identities, he gained attention by mixing off-color political commentary with deranged conspiracy theories, including one that the government wanted to implant Americans with microchips, and another that John F. Kennedy Jr., who died in a plane crash in 1999, was alive and about to replace Mike Pence as vice president.

“There was no nefarious intention behind it,” Mr. Hall said. “I was just trying to rally up MAGA supporters and have fun.”

Many of those “Make America Great Again” followers appeared to believe the posts. Records also show that some accounts served another purpose: directing people to give Mr. Hall money. They promoted a fund-raiser for a political group Mr. Hall created called “Gay Voices for Trump.” In an interview, he admitted that the group didn’t exist. The fund-raiser brought in more than $7,300.

Mr. Hall’s Twitter spree seems to be a case of mischief spun out of control, illustrating how a person simply needs a phone and some knowledge of the internet to start trouble that gets the attention of hundreds of thousands of people.

Mr. Hall was hardly the first self-professed Trump fan to try to profit off fellow Trump backers. Federal prosecutors, for example, said in August that Steve Bannon, President Trump’s former adviser, and three others had solicited donations to build a border wall and then pocketed more than $1 million.

And he was hardly the first person to create a fake online persona. Fake accounts have been instrumental in the spread of conspiracy theories, and scammers have repeatedly posed as celebrities, soldiers and even Mark Zuckerberg to defraud people on Facebook, Twitter and Instagram.

Those companies said they remove millions of fake profiles each year. Yet Mr. Hall showed that it was still fairly simple to impersonate key White House officials and the president’s family, including his teenage son, and amass tens of thousands of followers before Twitter took notice.

Millions of people have been lured down dark internet rabbit holes like QAnon, a pro-Trump conspiracy theory that claims satanic Democrats abuse and eat children and is fueled by someone posing as a government official. By comparison, Mr. Hall was a small-timer. His escapades in the alternate reality universe might have gone unnoticed — until Mr. Trump’s mistaken tweet elevated him to the big time of MAGA misinformation.

The New York Times identified Mr. Hall as the person behind the fake Trump accounts, which have now all been taken down by Twitter, and constructed a recap of his deception via screenshots of some of his tweets and an archive of many others collected by Ian Kennedy and Melinda Haughey, University of Washington researchers who use software to save millions of tweets about the election and pandemic. The Times also interviewed Mr. Hall, people close to him and people he misled online.

Mr. Hall said he became interested in politics in 2016 when he was a teenager, energized by Mr. Trump. “I kind of thought he was like a clown at first,” he said. “But the more I heard him talk, I realized: Yeah, he says kind of off-the-wall things, but I do agree with what he’s saying.”

He dreamed of becoming a conservative talk-radio host, he said, so he opted against college and decided to instead build a persona online. He sparred with liberals on Twitter; created a “public figure” page on Facebook; and self-published a 49-page e-book on Amazon called “Hall Nation” that detailed his “38 essential rules to live life in order to be happy and successful.” (The first rule? “Insults are a good thing.”)

Offline, he was not so successful. He struggled to hold a job, he said, including stints as a hotel clerk and sandwich maker. Most recently, he delivered food for DoorDash.

But online, he started to develop a small following. In January, he asked followers to help him pay for a lawyer, saying “a Planned Parenthood loving radical leftist” whom he used to date had accused him of harassment. He also began selling T-shirts that said “Josh Hall did nothing wrong.” He raised $815 on GoFundMe. Court documents indicate he is using a public defender. A hearing in the case is scheduled for later this month.

Mr. Hall said that around that time Twitter suspended his account without explanation. “Once I got banned from Twitter, my attitude was kind of like, ‘What the hell, I’m just going to have fun now,’” he said. (A Twitter spokesman said the company suspended his original account because he had created multiple accounts under different identities.)

So he started a new account under a different name: Rod Blagojevich, the former Democratic governor of Illinois best known for trying to sell a U.S. Senate seat. Mr. Blagojevich’s prison sentence had just been commuted by President Trump, making him a sudden ally in the eyes of some conservatives.

“OBAMA STARTED THE CORONAVIRUS,” Mr. Hall wrote on Feb. 27 under Mr. Blagojevich’s photo and a profile named @GovBlago. It was typical fare for the account, which eventually drew more than 26,000 followers. For much of the time it was active, the profile included a disclaimer in its bio that it was a parody account, which Twitter allows under some conditions.

The rest of Mr. Hall’s impostor accounts did not include such disclaimers.

Twitter eventually removed the @GovBlago account, prompting Mr. Hall to impersonate someone else in the headlines: Dr. Birx, the White House official working on the pandemic. “The media is lying to you about this virus,” he wrote as @DoctorBirx on April 22. The pandemic was “plotted by the powers that be to crash our economy in hopes that Trump will pay for it in November.”

The account didn’t gain much traction, so he moved on to a brand that was sure to attract more eyeballs: The Trump family. Mr. Hall said he went on Wikipedia to find Trump relatives who didn’t yet have Twitter accounts, and first landed on Robert Trump, the president’s brother.

As @BigRobTrump, he quickly gained more than 25,000 followers, partly by spreading conspiracy theories. “The coronavirus was planned and released onto the world by the Bill and Melinda Gates Foundation,” Mr. Hall said as Robert Trump. It was unclear if Mr. Hall believed such lies or if he thought they were just good at attracting attention, but they had become almost banalities in the conspiracy-filled corners of the internet where he spent much of his time.

When Twitter removed the first Robert Trump account, Mr. Hall started a new one, this time under the username @UncleRobTrump. It did even better, ultimately collecting more than 77,000 followers from July to August.

As the new Robert Trump account gained influence, Mr. Hall began using it to promote his own Twitter profile, @TheBiTrumpGuy.

On that account, Mr. Hall, who said he is bisexual, called himself the founder of a group called Gay Voices for Trump. Mr. Hall used the fake Robert Trump profile to promote the group.

“Uncle Rob runs Gay Voices For Trump with @TheBiTrumpGuy, although I am very much a heterosexual male. It’s the Trump genes – we love women,” Mr. Hall wrote as Robert Trump in July. “But we are trying to reach out to LGBT and other minority voters. Josh is doing great work so please give him a follow and support him!” The tweets brought Mr. Hall’s real profile thousands of new followers.

Not long after, Mr. Hall started messaging Trump supporters as Robert Trump, asking them to donate to a fund-raiser for his group, according to screenshots posted online by two people who received the messages.

“Hey patriot. Would really appreciate if you have a couple of bucks to spare to organization,” he wrote, according to one screenshot.

Mr. Hall denied he sent such messages and suggested that the screenshots had been fabricated. “I would tell you if I did,” he said. “I should have used better judgment and stuff. But I didn’t deliberately try and dupe people out of money.”

His fund-raiser on the website GoFundMe called his group “a grass-roots coalition of LGBT Americans” and said all donations would go to “field organizing, events and merchandise.” He brought in $7,384.

Mr. Hall admitted last week that the group didn’t exist. He didn’t do more than register about 100 people to vote. “I didn’t end up ever really doing anything with the Gay Voices for Trump,” he said. “So I never got the funds from it.” He said the money was still with GoFundMe.

A GoFundMe spokeswoman said that the organizer behind the fund-raiser — an account named Josh H. — had withdrawn the money. She said GoFundMe was now investigating how the funds were used and that the company would give refunds to any donors who requested one.

Mr. Hall didn’t respond to follow-up questions about the fund-raiser.

Josiah Bruns, an engineer from Goffstown, N.H., donated $100. With his donation, he left a comment: “Uncle Rob Trump asked me too.”

Mr. Bruns said in an interview that a QAnon message board had led him to the Robert Trump account, which also promoted the conspiracy theory. “We’re trained on the Q research board to always question everything,” he said, adding that he used those lessons to scrutinize the Robert Trump account. “I’m probably 65 percent sure that it was real.”

After The Times told Mr. Bruns that he had been deceived, he said he didn’t mind. In the future, he said, he would apply more research techniques he had learned from the QAnon movement to decipher what was real on the internet. The web is a minefield of lies, he said, “especially if it’s something you want to believe, because those are the easiest lies to fall for.”

In August, Robert Trump died. The news drew scrutiny to the fake Robert Trump account, and some of its followers began to suspect that Mr. Hall was behind it, given the pattern of tweets between the profiles. In response, Mr. Hall said on Twitter that the fake account was run by “a close political friend of mine” who “did not know about Mr. Trump’s serious condition.”

He began impersonating different Trump relatives, including Fred Trump III, the president’s nephew; Maryanne Trump Barry, the president’s sister and a federal judge; and Barron Trump, the president’s teenage son.

“COVID is a scam,” he wrote on Aug. 23 as Barron Trump, a fake account that attracted more than 34,000 followers in eight days. On Aug. 25, the account posted: “Q is real. The more the media delegitimizes it, the more it shows that they’re scared.”

The Trump Organization, which has spoken on behalf of the Trump family members in the past, did not respond to requests for comment. The White House declined to comment.

The Twitter spokesman said the company eventually took down all of Mr. Hall’s accounts for violating its rules on impersonation and evading a previous ban from the site. In response to questions about why someone could create accounts impersonating the president’s teenage son and a White House official, the spokesman said in an email, “We’re committed to protecting the integrity of the conversation on Twitter, and we’re working hard to ensure that violations of our rules against impersonation, particularly when people are attempting to spread misinformation, are addressed quickly and consistently.”

A review on Saturday showed nearly 100 fake Barron Trump accounts were still active on Twitter, not counting those that identified as parodies.

That left Mr. Hall feeling left out after the election, as many fellow Trump supporters convened on Twitter to claim that the vote was rigged. “Why not make a comeback?” he recalled thinking. “I’m going to do something to spice things up.”

On the afternoon of Wednesday, Nov. 18, he created a new impostor, this time posing as the father of Kamala Harris, the vice president-elect. “My daughter is not who she portrays herself to be. She is dangerous for our democracy,” he posted.

The tweet got little attention, so he abandoned that fake for another Trump sibling. The final living sibling he hadn’t tried was Ms. Trump Grau, the president’s older sister, who is in her late 70s, lives in Florida and has hardly said anything public since her brother was elected.

Mr. Hall changed the name, photos and bio of the Mr. Harris account and erased the old posts. Then he started with a new message: “This election inspired me to break my silence,” he wrote under a photo of Ms. Trump Grau and the username @TheBettyTrump. “My brother Don won this election.”

He went viral again, collecting about 20,000 followers in 24 hours. Mr. Hall delighted many of his followers with dozens more juvenile and bizarre tweets, including claims that President-elect Biden is a pathological liar, Ms. Harris is a communist and Michelle Obama is a man.

On Nov. 20, Mr. Hall said, he woke up and checked the president’s Twitter account, as he did most mornings. “I was like shellshocked,” he said.

He quickly began bragging on Snapchat that President Trump had tweeted about his fake account. “My friend was joking, ‘Maybe he’s not close with his sister, and you just brought him and his sister a lot closer,’” he said. “So I kind of felt good about that.”

Within hours, the account was outed as a fake.

Mr. Hall argued that his accounts were clear parodies, if anyone just looked at what they posted. As Ms. Trump Grau, for instance, he called the CNN anchor Anderson Cooper “Anderson Pooper” and said he would cover the legal fees of anyone who poured gravy down the pants of Chris Wallace, the Fox News anchor.

“I’m a big Trump supporter, but I’m thinking, ‘He’s got to know that that’s a parody,’” he said. “How does he not know?”