WASHINGTON — Faced with financial pressure and a federal investigation into his taxes and foreign consulting work, Hunter Biden has turned for money and strategic advice to an unlikely source: a wealthy Hollywood lawyer and novelist best known for brokering a lucrative licensing deal for the animated series “South Park.”

The lawyer, Kevin Morris, has quietly taken on an expansive role as a financier, confidant and would-be avenger for Mr. Biden, handling sensitive subjects for President Biden’s son that could have acute political ramifications for the White House.

Mr. Morris lent more than $2 million to Hunter Biden, which went to supporting his family and paying back taxes that are a subject of the ongoing federal investigation, according to four people familiar with the matter.

Mr. Morris advised Mr. Biden as he navigated a paternity and child support lawsuit, and helped him with his art career and a memoir published last year that was partly a response to attacks from former President Donald J. Trump.

He is funding a documentary project that is expected to build on the memoir’s redemption story, while depicting the president’s son as the victim of allies of Mr. Trump who distributed to the media a cache of files that appears to have come from a laptop abandoned by Mr. Biden in a Delaware repair shop.

Some of the tactics Mr. Morris is said to have advocated — like publicly questioning the story behind the laptop cache and attacking those involved in spreading files from it — have not been implemented. They have seemed at odds with the approach of Mr. Biden’s defense lawyers, who have proceeded cautiously while he is still under federal investigation.

Mr. Morris declined to be interviewed. Attempts to reach Hunter Biden through his lawyer were unsuccessful. The White House declined to comment.

Hunter Biden has a long history of seeking employment or profit in areas that overlapped with his father’s public duties and doing business with questionable partners around the world, including in Ukraine. His extensive and well-publicized personal travails — including addiction to crack cocaine, divorce, a relationship with his brother’s widow and money problems — have spilled into politics, helping to fuel relentless if largely baseless efforts by Republicans to link his father to his business ventures.

The criminal investigation into Hunter Biden’s taxes and international work appears to be coming to a head. Justice Department prosecutors have met in recent weeks to discuss whether to move forward with the case. In the coming months, the department is expected to make a final decision about whether to bring criminal or civil charges, or to reach some sort of settlement that could include a significant fine.

The decision will have to be approved by Attorney General Merrick B. Garland and will be among the most scrutinized of his tenure. Hovering over it is the possibility that Republicans will win control of Congress in November and immediately begin investigations into Hunter Biden and how the Justice Department handled the case.

The White House has said it has no role in advising Hunter Biden on his legal problems or on his public messaging. Mr. Morris’s emergence as an influential adviser underscores the delicate situation that President Biden has to confront with the issues swirling around his son.

On one hand, Mr. Biden’s use of Mr. Morris’s loan to pay back taxes could make it more difficult to prosecute a criminal tax case against the president’s son. And the president’s confidants see Mr. Morris as a key member of Hunter Biden’s emotional inner circle, a friendly shoulder to lean on as he navigates the federal investigation while trying to rebuild his life after the death of his brother, Beau, and struggles with drug addiction.

At the same time, some of the president’s allies see Mr. Morris as a potential liability. They are uneasy with his many ideas about how to go on the offense publicly, a person familiar with their thinking said. And they are concerned that it could reflect badly on the administration for the president’s son to be receiving financial assistance from a wealthy benefactor — a dynamic that could evoke the payments, which are now under scrutiny from federal prosecutors, that Hunter Biden accepted from a Ukrainian oligarch’s company and other foreign interests.

The allies prefer that the president’s son continue to keep a low profile and follow exactly what his primary defense lawyer, Chris Clark, tells him to do. They want Hunter Biden to do whatever he can to settle the matter with the Justice Department if prosecutors decide they want to charge him, according to the person familiar with their thinking.

Mr. Morris’s assistance is motivated less by any political calculus than by “a tremendous empathy for people who were struggling,” said Glenn C. Altschuler, an author and professor at Cornell University who mentored Mr. Morris as an undergraduate and has stayed in close contact with him since.

“He’s got a heart as a big as a house, and as his wallet has expanded, he’s been able to make his sympathies, his empathy, manifest in a variety of ways,” Mr. Altschuler said.

Mr. Morris, 58, made a big splash in Hollywood, and a lot of money, when he negotiated a landmark deal that gave the creators of “South Park,” Matt Stone and Trey Parker, a precedent-setting 50 percent stake in the cartoon’s success in digital media.

Mr. Morris had met the pair years earlier when they were relatively little-known filmmakers, and he represented them for the next few years for free. He later produced a musical, “The Book of Mormon,” that the pair had written with a third partner for which he won a Tony Award.

Mr. Morris has also written a show-business satire called “Gettysburg,” a semi-autobiographical coming-of-age tale titled “All Joe Knight,” and a collection of short stories.

Mr. Morris met Hunter Biden, now 52, in December 2019 at a fund-raiser for the Biden presidential campaign, and soon developed an almost paternal affection for Mr. Biden, according to an associate of Mr. Morris. Mr. Morris’s relationship with Mr. Biden was first reported by CBS News.

At the time of their initial meeting, Hunter Biden was working to get his life back together. Mr. Biden was under attack from Mr. Trump and his allies, who were seizing on his personal struggles and foreign business dealings to try to undermine his father’s campaign for the Democratic presidential nomination.

Mr. Biden and Mr. Morris both lived in Los Angeles and became close, with Mr. Morris assisting as Mr. Biden worked to finish a memoir. It detailed his struggles with addiction and loss and credited his new wife, Melissa Cohen, with pulling him back from the brink of despair and self-destruction. It also pushed back against Mr. Trump’s attacks on him and his family.

Mr. Morris, who had donated $2,800 to the Biden campaign before meeting the candidate’s son, donated $55,000 to super PACs supporting the campaign and opposing Mr. Trump in the months after the meeting — exponentially more than he had given to federal committees previously, according to campaign finance records.

As a young man, Mr. Morris worked as an office assistant for a member of the British Parliament, but he has little discernible experience in American politics.

Mr. Morris — who produced a 1997 film called “Hands on a Hardbody: The Documentary,” about an annual competition in Texas to see who can keep their hand on a pickup truck longest — has begun developing the idea and collecting footage for a film featuring Mr. Biden. It is being produced by a company Mr. Morris started last year called Media Courthouse Documentary Collective. The company is also producing films on subjects including cryptology, Congress and the unfolding defamation case brought by Johnny Depp against his ex-wife, the actress Amber Heard.

While the documentary about Mr. Biden is still in the formative stages, according to people familiar with it, they said it could seek to undermine attacks on its subject while also advancing the story of his redemption, including focusing on the launch of Mr. Biden’s career as an artist.

Mr. Morris, who collects art, has encouraged Mr. Biden’s art and owns some of it, according to two people familiar with his collection, though one suggested the art might have been given to him as a gift.

While Hunter Biden previously told The New York Times that his painting “is literally keeping me sane,” it has caused headaches for the administration. The White House helped develop a set of ethics guidelines intended to keep the identity of buyers of Mr. Biden’s art, and other details of the sales, from both the artist and the administration. That came after criticism over a gallery show in SoHo at which asking prices were between $75,000 and $500,000 per piece — high for a novice artist.

Mr. Morris and a man with a video camera were photographed following Mr. Biden and Ms. Cohen outside the SoHo gallery at the opening of Mr. Biden’s show, which was attended by President Biden’s sister and other family members.

Plans for the documentary also include raising questions about the veracity of the story behind the cache of emails, text messages and other files from Hunter Biden’s accounts that were obtained and disseminated to the media initially by Rudolph W. Giuliani.

The New York Times and other media outlets have authenticated some of the files, which detailed Mr. Biden’s finances and his work for foreign individuals and companies at a time when his father was vice president and was overseeing elements of American foreign policy that overlapped with the interests of Hunter Biden’s clients.

Some of those files have come under scrutiny from prosecutors investigating Hunter Biden for possible violations of tax, money laundering and foreign-lobbying laws.

Mr. Morris has privately questioned whether the files all came from the laptop abandoned in Delaware or were spliced together from an array of sources. He has also indicated that the Justice Department should investigate the chain of custody.

He has circulated diagrams showing a set of Trump allies who have been involved in disseminating the files, including the former White House adviser Stephen K. Bannon, the former personal lawyer Mr. Giuliani and the Chinese billionaire and Mar-a-Lago member Guo Wengui.