The lawyer at the centre of the whistle-blower complaint is one of Trump's most vocal and defiant supporters.
A whistle-blower described him as a "central figure" in an effort by US President Donald Trump to "solicit interference from a foreign country in the 2020 US election". He maintains he has done nothing wrong. Rudolph "Rudy" Giuliani, Trump's personal lawyer, remains one of the president's most recognisable and steadfast allies, and as the impeachment inquiry into Trump got under way, he was one of the first individuals House Democrats subpoenaed for documents.
Giuliani has acknowledged he spoke to Ukrainian officials and broadly asked them to investigate Joe Biden, a 2020 Democratic presidential frontrunner, and his son.
"Of course I did," Giuliani told CNN last month, seconds after saying that he didn't ask Ukraine to look into Biden.
Those interactions and others described in the whistle-blower complaint are now under higher scrutiny as part of an impeachment inquiry into the president. And House Democrats have demanded he turn over documents related to his communications with Ukrainian officials.
Giuliani meanwhile has continued to make his rounds on cable news channels, standing by the president and his endeavours on Trump's behalf, and calling the whistle-blower complaint "crap" while insisting that history will one day pronounce him a "hero".
A target of derision for the president's critics, however, Giuliani's path from nationally-known Republican, New York City politician to Trump's most reliable cable news defender marks him as an unusual figure: a Republican politician who ascended to power in one of the US's most liberal cities, a public figure once thought fit for the presidency whose public appearances now invite heckling, and a former tough-on-crime crusader who placed himself at the centre of an ever-expanding constellation of presidential corruption scandals.
From Democrat to Republican
The grandson of Italian immigrants who settled in New York City in the early 20th century, Giuliani reportedly considered entering the priesthood as a young man before attending New York University School of Law, graduating in 1968. At the time, the young Giuliani was a Democrat, reportedly voting for the anti-Vietnam War Democrat George McGovern in 1972.
Giuliani's rightward journey through the 1970s and 80s paralleled his professional success. He joined the staff of Deputy Attorney General Harold "Ace" Tyler under then-Republican President Gerald Ford.
Then-New York Mayor-elect Rudy Giuliani celebrates his election win against Mayor David Dinkins [File: Mark Lennihan/AP]
By the time then-President Ronald Regan named Giuliani to the position of US attorney for the Southern District of New York in 1983 he had registered as a Republican.
It was unclear to what extent this signified a genuine political conversion at the time. In an unpublished 1988 interview quoted in the Wayne Barrett biography Rudy!, Giuliani's mother said her son "only became a Republican after he began to get all these jobs from them. He's definitely not a conservative Republican. He thinks he is, but he isn't. He still feels very sorry for the poor."
As US attorney, he agressively prosecuted New York mafia families.
New York City mayor
Giuliani was elected mayor of New York City in 1993, the first Republican to occupy the city's mayoral seat since 1965. Propelled into office by capitalising on a conservative backlash against the city's first African American mayor, Democrat David Dinkins, Giuliani described his city in apocalyptic terms, as a lawless place in need of a firm governing hand.
His vitriol focused on minority communities in particular. Speaking about the city's black elected officials in 1994, Giuliani reportedly said "they're going to have to learn how to discipline themselves in the way in which they speak also".
Then-Mayor Rudy Giuliani gestures as he announces that New York City appears to be leading the nation's fight against crime [File: Todd Plitt/AP]
Giuliani's time as New York City mayor is perhaps best remembered for its hyperfocus on law and order. Between 1993 and 2001, the murder rate fell from 1,927 in 1993 to 643 in 2001. Though widely credited for inspiring a renewed sense of security among New York City residents, the feeling was not shared by many in the city's minority communities, who disproportionately bore the brunt of police harassment, regular "stop and frisk" searches, arrests for minor crimes, and episodes of grave physical brutality. Giuliani, meanwhile, repeatedly defended the city's police department.
Arguably Giuliani's brightest moment as mayor would take place during his city's darkest period in recent memory: the September 11, 2001, attacks on the World Trade Center. His reassuring presence in the streets that day earned him the title of "America's mayor" and the title of Time's Person of the Year in 2001.
Armed with a surge of goodwill, Giuliani launched a bid for the Republican presidential nomination in 2008, only to find himself unpalatable to the party's ultra-conservative base, who frowned at his pro-choice views on abortion and tolerance of the LGBT community. He suffered from corruption allegations and reported lobbying ties that ran counter to American national security policy.
Then-Republican presidential hopeful Rudy Giuliani holds a town hall meeting during a campaign stop at New England College in New Hampshire [File: Jim Cole/AP]
When he failed to secure the nomination, it seemed that Giuliani's political career might be over. But the election of fellow celebrity New Yorker Trump to the presidency nearly a decade later offered Giuliani a chance for a resurgence.
In August 2018, Giuliani joined Trump's legal team. His responsibility as Trump's top lawyer was to bring Special Counsel Robert Mueller's investigation into Russian interference in the US presidential election to an end.
To do so, Giuliani began making regular appearances on cable news, defending Trump against allegations of wrongdoing with an array of ever-changing narratives. At one point, during an interview with Meet the Press's Chuck Todd in August 2019, Giuliani argued against having Trump sit down for an interview with Mueller, saying that "truth isn't truth". Outbursts of this sort were widely derided by the president's critics and across social media.
If Giuliani's arguments on behalf of Trump frequently appeared incoherent or downright lethal for the president's defence strategy - he once went as far as to say that collusion with Russia to win an election is not illegal, before later clarifying "my client didn't do it, and even if he did it, it's not a crime" - Mueller's conclusion not to charge Trump with a crime only strengthened Giuliani's resolve to stand by Trump.
Determined to expose the Russia investigation as the product of a Democratic plot to unseat Trump, Giuliani embarked on an international campaign to demonstrate that it was actually Trump's opponents who deserved scrutiny for corruption on an international scale.
In May, Giuliani told the New York Times that he had plans to travel to Ukraine to dig up information that he hoped would discredit the Mueller investigation. He also said he was going to encourage the then-Ukrainian president-elect to investigate Biden and his son despite there being no evidence of wrongdoing by the former vice president or his son. Hunter Biden, the former vice president's son, served on a board of a Ukrainian gas company around the same time his father was leading the Obama administration's efforts in Kiev.
During the May interview with the New York Times, Giuliani said Trump was aware of his efforts "as his lawyer", before somewhat walked back on those comments in August, when he said he was working as a private citizen. Giuliani has also said that the State Department was aware of his efforts in Ukraine.
News reports would continue to allege that Trump was personally involved in attempts to investigate Biden - with the Wall Street Journal reporting that Trump pressured Ukrainian president Volodymyr Zelensky to work with Giuliani on an investigation into Hunter Biden in a July phone call.
More details would come to light in late September, when House Intelligence Committee chair Adam Schiff publicly released a whistle-blower complaint filed in August by an unnamed intelligence officer.
The complaint alleges that Trump used "the power of his office to solicit interference from a foreign country in the 2020 US election" by attempting to prompt a Ukrainian government investigation of the Bidens. The complaint alleges Giuliani "is a central figure in this effort".
Giuliani delivers remarks before Donald Trump rallies with supporters in Council Bluffs, Iowa [File: Jonathan Ernst/Reuters]
According to the whistle-blower, who cited US officials, Giuliani held meetings with Ukraine's chief prosecutor in New York and Warsaw, Poland, and that "associates" of his met the head of Ukraine's security service and an adviser to Zelensky. Over the course of these exchanges, Ukrainian government officials came to understand that the success of their relations with the US government would depend on their president's willingness to "play ball", the whistle-blower said. In July, claims the whistle-blower, they learned that Trump instructed the suspension of all US military aid to Ukraine - though it would eventually be released as planned.
Zelensky and Trump eventually spoke over the phone on July 25, and a week later, Giuliani reportedly travelled to Spain for a meeting with an aide to the Ukrainian president to talk about the issues discussed in that phone call, the complaint said.
The complaint and the Trump administration's actions surrounding it prompted Democrats to launch an impeachment inquiry of the president. Trump has repeatedly denied any wrongdoing, calling the inquiry "witch-hunt garbage".
In the aftermath of the complaint's public release, Giuliani continued to make himself available to cable news networks to defend Trump. Giuliani confirmed he asked Ukraine to investigate Hunter Biden in an interview with CNN, called a fellow panelist on a Fox News show a "moron" for questioning his claims against the Biden family, and tweeted out personal text messages between himself and the US's special representative to Ukraine Kurt Volker, suggesting he liaised with Ukrainian officials with State Department approval. The State Department has denied any wrongdoing. Volker has since resigned from his post.
If anything, these attempts at defending himself have only landed Giuliani in more hot water, with critics of the president like senator and Democratic presidential candidate Kamala Harris calling for further investigation into Trump's use of diplomacy for personal ends and a subpoena arriving at Giuliani's doorstep.
Giuliani, on the other hand, is as defiant and bellicose as ever, not only claiming that he is "the real whistle-blower", but also suggesting he could sue House Democrats over their investigation.
Trump Lawyer Rudy Giuliani