Hunter Biden, middle child of Democratic presidential nominee Joe Biden, spoke at the fourth and final night of the Democratic National Convention

Joe Biden was sworn into office for a Delaware Senate seat in a Wilmington, Delaware, hospital where his two young sons, Hunter and his brother Beau, were taken after being severely injured in a car accident that killed Biden's wife and baby daughter, Naomi, in 1972.

The senator's daily 90-minute train commute to Washington, DC, and back to Delaware to care for his sons earned him the nickname "Amtrak Joe."

Biden later married Jill Jacobs, Hunter and Beau's stepmother, in 1977. The brothers' half-sister, Ashley, was born on June 8, 1981.

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CNN reported that Hunter Biden resigned from the firm when then-Sen. Barack Obama, who said he would refuse donations from lobbyists, asked Joe Biden to join his presidential ticket.

Hunter Biden later told The New Yorker that no one from the Obama campaign had directly told him to break his lobbying ties but that he knew "the writing was on the wall," so he resigned from the firm and from an unpaid seat on the Amtrak board in preparation for the election.

"I wanted my father to have a clean slate," Hunter Biden told the outlet. "I didn't want to limit him in any way."

In September 2008, Hunter Biden launched a consulting firm, Seneca Global Advisors, and in June 2009, Hunter cofounded the private-equity firm Rosemont Seneca Partners. The New Yorker said that through his companies and his partners, Hunter Biden established various business connections to figures in China and Russia.

His blooming international business relationships came to a head when his father adopted policy priorities to crack down on corruption in Ukraine, but he was not accused of any formal wrongdoing.

Hunter Biden's tumultuous personal life became tabloid fodder during and after his father's time with the administration.

He sparked confusion when he, then 44 years old, enlisted in the Navy Reserves in 2012, less than two years before reports broke that the Reserve discharged him in 2014 after he tested positive for cocaine.

Hunter Biden eventually confirmed the news and said in a statement that it was "the honor of my life to serve in the U.S. Navy, and I deeply regret and am embarrassed that my actions led to my administrative discharge. I respect the Navy's decision. With the love and support of my family, I'm moving forward."

After tragedy struck the family through 46-year-old Beau Biden's death from cancer in 2015, Hunter Biden's personal life remained in the headlines.

After he divorced his first wife and the mother of his three daughters, Kathleen, the Biden family acknowledged he was dating Hallie Biden, Beau's widow.

Hunter Biden raised eyebrows with a candid New Yorker interview in which he said he spent the aftermath of his brother's death on a bender that included him buying crack from homeless people. He also said that he and Hallie Biden discovered they were "sharing a very specific grief" and spent a lot of time together in 2016 before they became a couple.

The couple apparently tried to keep the relationship secret, but the former vice president found out when Page Six called him for comment on a story on the relationship, after which he and Jill Biden issued a supportive statement.

"We are all lucky that Hunter and Hallie found each other as they were putting their lives together again after such sadness," the statement said. "They have mine and Jill's full and complete support and we are happy for them."

It's unclear when Hunter and Hallie Biden stopped dating, but their breakup was reported in early May, shortly before TMZ reported the "secret" wedding between Hunter Biden and the South African model Melissa Cohen, which happened on May 16.

Within one month of his term on the board expiring, a bombshell New York Times story published on May 1 detailed Joe and Hunter Biden's ties to Ukraine and said the former vice president had successfully gotten a Ukrainian prosecutor removed from office.

The move raised questions about a possible conflict of interest and if Joe Biden was trying to shield his son from an investigation into the company, whose founder faced multiple investigations into allegations of tax evasion and money laundering.

The former vice president was reported to be just one part of a larger push coming from former President Obama's administration for the Ukrainian prosecutor Viktor Shokin to be removed over concerns of corruption in his office. Joe Biden has since publicly detailed his threat to withhold $1 billion in loan guarantees from the country if Shokin wasn't fired.

However, it's since been reported that there was not an active investigation into Hunter Biden when the former vice president made the push for Shokin's firing, and Yuriy Lutsenko, Ukraine's prosecutor general, later said that he had no evidence of wrongdoing against either Biden.

Despite the absence of proven wrongdoing by the Bidens, the back-and-forth has been used by the Trump administration to obscure Rudy Giuliani's communications with Ukraine that were made public earlier this year and the growing concern that Trump actively collaborated with a foreign power to gain political leverage.

Hunter Biden delivered a speech on the final night of the Democratic National Convention, where his father accepted the nomination for the Democratic presidential nominee.

Ashley and Hunter Biden gave an emotional remark prior to his speech, "he's been a great father," Hunter Biden said. "And we think he'll be a great president," his sister followed. The two addressed the death of their older bother Beau, who introduced their father at the 2008 and 2012 conventions.

-ABC News (@ABC) August 21, 2020