George Nader, a mysterious business executive with links to the United Arab Emirates and a key figure in Trumpworld, seems to be popping up more and more in reports about the Russia investigation.

Nader, a Lebanese American who has acted as a mediator and back-channel diplomat in Middle Eastern affairs for decades, has reportedly agreed to cooperate with special counsel Robert Mueller’s probe into the Trump campaign’s ties to Russia in exchange for immunity.

It’s possible that Nader has valuable information on the Trump transition team’s meetings with foreign officials that have puzzled investigators for months. And Mueller’s investigators are looking into how he may have funneled Emirati money to a top Trump fundraiser to influence the White House’s Middle East policy.

As the Associated Press reports, the Mueller probe is especially interested in two meetings in particular that occurred while Nader was serving as an adviser to the UAE. The first is a meeting he attended in Trump Tower in New York in December 2016 with Jared Kushner; Steve Bannon, who was then Trump’s chief strategist; and Mohammed bin Zayed, the UAE’s de facto ruler.

The second event was in January 2017 in Seychelles, a collection of islands in the Indian Ocean. That meeting included Nader; bin Zayed; Kirill Dmitriev, a Russian fund manager with close ties to Russian President Vladimir Putin; and Erik Prince, the founder of the private security firm Blackwater and an informal adviser to the Trump transition team.

The Mueller probe is also investigating how Nader might have helped the UAE buy political influence in the Trump White House by striking huge business deals with a top Trump fundraiser. That raises the question of whether Mueller’s probe is casting a wider net to track the possible influence of countries other than Russia on Trumpworld.

What follows is a brief guide to Nader’s shady past and why it seems like Mueller has taken an interest in him.

Nader could be very valuable to Mueller’s investigation

Nader was born in Lebanon and came to the US in his teens. He has worked as a fixer for the US and foreign governments, quietly brokering deals across the Middle East for decades. He served as an informal envoy to Syria for the Clinton administration and worked as a negotiator to help free US hostages in Lebanon. In the past few years, he has served as a political adviser to the UAE.

Nader also has a criminal record. In 1991, he pleaded guilty to a federal child pornography charge in the US, and he was convicted in the Czech Republic of 10 cases of sexually abusing minors in 2003.

The globe-trotting power broker could be a key source of information for the Mueller probe for a number of reasons. The Seychelles meeting is of special interest regarding the question of collusion with Russia. Prince, the Blackwater founder, has denied that he was representing the Trump transition team during the meeting. And Dmitriev, the Russian fund manager, has described it as an informal and friendly gathering.

But Nader could shed more light on what actually went down and if any covert deals were discussed. He could, for example, testify as to whether Prince and Dmitriev discussed any kind of quid pro quo between Putin and Trump tied to Russia’s meddling in the 2016 election.

Nader’s cooperation with the probe also gives Mueller insight into how other countries may have attempted to influence the White House — and whether corruption was a factor.

Nader seems to have used some potentially questionable tactics to lobby for Middle Eastern countries. Around the time of Trump’s inauguration, he met Elliott Broidy, a business executive and a top Trump fundraiser. They quickly developed a collegial relationship, and Nader appealed to Broidy’s personal business interests to gain influence with the White House.

Nader helped connect Broidy to some new potential clients for Broidy’s private security company, Circinus: the UAE and Saudi Arabia. He helped deliver more than $200 million in contracts for Circinus with the UAE and has recently been in talks with Broidy to set up a $650 million contract with Saudi Arabia.

They then discussed how Broidy could use his influence in Washington to lobby on behalf of Saudi and Emirati foreign policy objectives, like taking a hard line against Qatar and Iran.

Just weeks after Nader wired $2.5 million to Broidy through a company in Canada, Broidy began making large donations to members of Congress who were backing legislation critical of Qatar.

Last fall, Broidy sent Nader a memo detailing how, in a private meeting with Trump in the Oval Office, he had pushed for the president to meet with bin Zayed and support his foreign policy goals in the region. He had also urged Trump to fire then-Secretary of State Rex Tillerson.

Nader also met with Bannon and Kushner during the transition between the Obama and Trump administrations at least once, and also regularly during the early months of the presidency — including in May, right before Trump’s trip to Saudi Arabia.

It’s unclear what they discussed during those meetings, but given Nader’s style of using business deals to score political points, investigators are surely looking for signs of foul play.

Given all of his connections and his unorthodox lobbying style, Nader could be a gold mine for the Mueller probe.