She's known as the "Cryptoqueen" who defrauded billions through a cryptocurrency which had no real value before disappearing.  

Now she's got a target on her back, with the Federal Bureau of Investigation (FBI) adding her to its list of 10 most-wanted fugitives. 

Ruja Ignatova is the 11th woman in history to be added to the list and she sits among murderers and gang leaders. 

So who exactly is the 'Cryptoqueen'? 

Born on May 30, 1980, in Sofia, Bulgaria, Ignatova spent most of her youth in Schramberg, Germany, before earning a PhD at the University of Constance. 

She studied international law in 2005 and wrote a dissertation discussing conflict law.

Following her study, Dr Ignatova worked at global management consultancy firm McKinsey & Co before investing with Icelandic model Asdis Ran in her fashion business, Ice Queen, by the time she was 31.

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However, her troubles started soon after

In 2012 she was convicted of fraud in Germany for taking part in delaying the insolvency of the Waltenhofen casting plant with her father Plamen Ignatov, according to local media. 

She was also linked to BigCoin, a failed multi-level marketing cryptocurrency, in 2013. 

But she is most famous for cryptocurrency Ponzi scheme OneCoin.

It was said to be the 'Bitcoin killer'

OneCoin was labelled as the "future of money" — a new cryptocurrency that promised to be the world's biggest.

Dr Ignatova launched OneCoin in 2014 with Sebastian Greenwood, who is currently in prison awaiting trial. By 2017 there was more than $US4 billion ($5.8 billion) invested in the cryptocurrency.

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Dr Ignatova's success reached its peak in 2016 when, aged 36, she presented OneCoin on stage at London's Wembley Stadium where she promised the cryptocurrency would "transform the life of unbanked people".

She went on to tour the world hoping to attract more investors. 

But there was an essential piece of information missing

There was no blockchain, a piece of information which keeps a record of transactions made by cryptocurrencies, according to the FBI.

"OneCoin claimed to have a private blockchain," Special Agent Ronald Shimko said.

"This is in contrast to other virtual currencies, which have a decentralised and public blockchain. 

 This meant the coin had no real value.

According to prosecutors, sales of the coin worked like a pyramid scheme, where members were commissioned to recruit others to purchase the worthless cryptocurrency.

Why is she wanted by the FBI?

The "Cryptoqueen" was charged in a New York court and a federal warrant for her arrest was issued in 2017.

On February 6, 2018, a superseding indictment was issued charging Dr Ignatova with one count each of conspiracy to commit wire fraud, wire fraud, conspiracy to commit money laundering, conspiracy to commit securities fraud, and securities fraud.

But she has never fronted court.

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In fact, Dr Ignatova has been missing ever since she boarded a flight in Bulgaria to Greece in 2017.

She has also been on the Europol most-wanted list, however, but is no longer featured.

The FBI is offering a $US100,000 reward ($145,000) for information leading to her arrest.

It is believed the now 42-year-old may be travelling with armed guards or associates and she may have had plastic surgery. 

The FBI also notes she speaks English, German and Bulgarian and may be travelling on a fraudulent passport.

Who else was involved? 

Following Dr Ignatova's disappearance, her brother Konstantin Ignatov became the public face of OneCoin.

He pleaded guilty in 2019 to charges of money laundering and fraud, and is waiting to be sentenced for the crimes. 

He testified in court in 2017 that his sister had become suspicious of her then-boyfriend, Gilbert Armenta, a married man she planned to elope with. 

Her instincts were right — she discovered he was working as an FBI informant.

She left the country soon after and has not been seen since.

Armenta has pleaded guilty to conspiracy to commit wire fraud, conspiracy to commit money laundering and conspiracy to commit extortion all relating to OneCoin. He is waiting to be sentenced.

Also involved was OneCoin lawyer Mark Scott who was convicted of defrauding $US400 million, however, he is appealing that charge.

Who else is on the FBI most-wanted list?

Dr Ignatova joins Arnold Jimenez, who is wanted for allegedly killing his wife in 2012, Alex Flores, who is believed to have kidnapped and murdered a five-year-old in 2000, Jose Rodolfo Villarreal-Hernandez, who is wanted for allegedly directing individuals to track and murder a man in Southlake, Texas, and Yulan Adonay Archaga Carias, the alleged leader of criminal gang MS-13 in Honduras.

Also on the list are Rafael Caro-Quintero, who is considered a godfather of Mexican drug trafficking and is wanted for the 1985 murder of a US federal agent, accused murderers Eugene Palmer, Bhadreshkumar Chetanbhai Patel and Alejandro Rosales Castillo, and also Jason Derek Brown, who is wanted for murder and armed robbery.

with wires